Just before Judy could reach the Buchatti, Nick suddenly pulled her back with the paw she was still tightly holding onto. "Ease up a minute, Carrots," he said, sounding slightly out-of-breath from their sprint across the impound lot.

Nick pulled his paw free and then shrugged his suit jacket off, turning it inside out to reveal a lining mostly made of pale blue silk. Before Judy could ask what he was doing, he was rubbing what had previously been the exterior of his jacket against her head. "Nick!" Judy protested, her voice shrill in surprise as she moved against his vigorous scrubbing, but he cut her off.

"Stop squirming," he said, "Do you have any idea how much of that river muck you have on you?"

"Nick—" Judy began again in a more normal tone.

"Ah ah ah," he cut her off again, and while she couldn't see his face with the jacket covering her head, she thought that he might be smiling, "This is your fault for ruining my handkerchief."

Judy offered no further protestations, and she could feel the wool of Nick's suit taking away clumps of filth she didn't want to think too closely about as his large paws massaged the fabric. Once she had gotten past the surprise of how suddenly he had done it, the feeling was almost pleasant, like when he had stroked her ears. Eventually, though, Nick seemed to decide that he was done and he draped his jacket across her shoulders. In much the same fashion as the shirt of his that she had borrowed, the suit jacket was far too long for her, and Nick stepped back and looked at her with a critical eye.

"That'll keep the interior of the car clean," he said, nodding his approval.

Judy looked down at herself and saw that what was visible of her own clothes looked entirely ruined. Nick chuckled as her ears drooped. Her outfit had come from the department store on the shopping trip that Nick had paid for, and it hadn't been cheap; she felt terrible about ruining it. "Besides, I can't have you dying of dysentery after you marinated yourself in that—"

"Thank you," Judy said quickly, cutting him off.

Nick gestured dismissively. "I mean it," Judy said, "For everything."

Nick climbed into the Buchatti. "Don't thank me yet," he warned, "You might still get sick."

Despite his warning, there was still a smile on his face, and it didn't fade even as Judy started the car and they headed for the address that had been inside Scursly's cigarette case.

Judy had never been to the Rainforest District before, but she knew enough about how Zootopia was laid out to anticipate that the address would be there. She was looking forward to seeing it, as she had of course never seen a real rainforest before either, and as they approached the wall that separated the district from the rest of the city didn't look too different from the one at the border of Sahara Square. As they got closer, though, Judy saw that many of the gleaming steel panels had been removed, exposing an absolute maze of pipes that looked about as tangled as a plate of spaghetti. Her first thought as they entered the Rainforest District was that there was maintenance ongoing, as there was absolutely no difference in temperature or humidity as they crossed the threshold of the gate, and the part of the city on the other side looked nothing like what she had expected.

From reading about the Rainforest District, Judy had expected it to be almost unbearably hot and humid, full of lush green vegetation and beautiful flowers kept blooming by an elaborate series of heaters and sprinklers hidden throughout. However, all of the vegetation that she could see was either dead or dying. There was a massive grid of pipes, designed so that they almost looked like tree branches, suspended about forty feet above street level. Clearly, the pipes were where the water was supposed to come from, but the ground was totally dry and covered with a thin layer of wilted brown leaves that had fallen from dying vines that ran along buildings or had been wrapped around the pipes overhead. Dying streamers of vegetation peeled away from buildings, and the moss that covered everything made of wood, which included a fair number of the buildings and railings that ran along the sidewalks, was a sickly brown color rather than a lush green.

Some of the buildings had been designed so that they looked like trees, with sides textured like bark, but the lack of healthy vegetation made them look not just obviously fake but somehow pathetic. There was a billboard (dying tendrils wrapped around the pole supporting it) that immediately explained why the Rainforest District looked so terrible. In large white letters against a vivid red background it read "POLIO OUTBREAK!"

In smaller, though equally legible letters, there was the note, "TAKE EXTREME PRECAUTIONS WITH CHILDREN."

As they continued driving towards their destination, there were other signs of the polio outbreak. Some apartment buildings they passed had red quarantine placards on their front doors, and there were signs with admonishments like "SPITTING PROHIBITED BY PUBLIC ORDINANCE" and "CHECK YOUR PIPES! BOIL ALL WATER FOR DRINKING!"

Judy remembered having read in the newspaper about an ongoing polio outbreak in the Rainforest District about a week or two ago, but she had never imagined the effect that it would have. The control system to make it an artificial rainforest had clearly been shut off to help stop the spread of the disease, and it must have been off for more than a month for the vegetation to be so dead. The district seemed eerily empty, too, with almost no mammals on the streets and lots of buildings that looked as though they had been all but abandoned. Considering the risk that polio posed to mammals, and particularly young ones, Judy couldn't blame anyone who had left.

Still, even by the depressing standards of the Rainforest District in its current state, the Canopy Hotel looked run-down and seedy. The Canopy Hotel's closest neighbors included an equally seedy-looking pawn shop and a gas station so dirty that it looked as though it had never been cleaned. The hotel was a long, squat building only two stories tall, with a rotting veranda wrapped around it and outer walls covered in dying moss and lichen. A rusty sign affixed to the side of the building had the hotel's name above a painting of a rainforest in far better health than the district was, but even if the vegetation was alive Judy doubted the view from the Canopy Hotel would even come close to the image.

Judy parked the Buchatti near the entrance and got out of the car and turned to Nick. "I had no idea the polio outbreak had gotten this bad," she said.

Nick simply shrugged. "The mammals who can afford to leave, leave. Everyone else stays and rolls the dice," he said, and from his tone Judy was certain that he had been one of the mammals who had had to stay when he had been a kit.

"It's not fair," she said quietly, and Nick nodded.

"What is?" he asked, and Judy didn't have an answer.

The interior of the hotel looked just as bad as the outside. The hotel rooms themselves all had doors leading to the veranda wrapped around the building, so the interior was simply a cramped lobby, a couple of bathrooms, and a door that led to what was probably a kitchenette. The grout between the tiles of the lobby's floor had gone a disgusting greenish-brown with mold, and the cheap wood paneling along the walls had warped, probably from when the district's climate control had been active and the humidity had been high. The only furniture in the lobby was a desk made out of panels of wood identical to the ones lining the walls and equally warped, and behind it sat a fat tapir reading a newspaper.

"Excuse me?" Judy said, pulling out her badge and trying to catch the attention of the clerk at the hotel's front desk.

The tapir, who looked to be about middle-aged and was positively squeezed into his uniform of faded and stained blue velvet, heaved a sigh and just barely lowered the paper. He didn't seem to notice her Prohibition Agent badge, his eyes instead darting from her to Nick. "Ten cents an hour or fifty cents a night," he said, "You or that goof of yours break anything you pay for it, ya understand?"

He had said the word with a deliberate and obvious sneer, and Judy could feel her ears flushing as the tapir leered at them. "I'm not— We're not—" she sputtered, and then remembered that she had her badge out.

"I'm a Prohibition Agent," she managed at last, raising her badge a bit more.

The tapir folded his paper and set it down. "A bunny prohi?" he said, and the skepticism in his voice was obvious, "With a fox? Dressed like that? Look, lady, keep me outta whatever kind of game the two of yous is playin'. You wanna room or not?"

Nick stepped forward. "That's a real badge, you know," he said in a conspiratorial tone, leaning against the desk, "And this is a real investigation."

The tapir snorted hard enough to send his jowls and sizable snout wiggling. "An' I ain't touched a drop in my life," he said, rolling his eyes, "'Investigate' all ya like, but don't do it in here. Beat it, pal."

Judy had no idea what she could possibly say to convince the tapir that she really was a prohi, short of trying to arrest him, but Nick stood back up and gently grabbed Judy by the elbow. "Come on, Sweetheart," he said, tipping her a wink as they made their way out of the lobby.

As they left, Judy could hear the tapir muttering something that sounded like, "Goddamn freaks."

Once they were outside, Judy crossed her arms across her chest, hating how childish she felt wearing Nick's oversized suit jacket. "There'll still be mammals like him even if you're wearing a police uniform," Nick said, and Judy sighed, her frustration evaporating.

Judy had seen for herself how poorly Nick got treated simply because he was a fox, and by comparison it seemed selfish to complain about mammals not taking her seriously because she was a bunny. Still, Nick was looking at her sympathetically, and she said, "I know."

Nick was silent a moment before he spoke again. "You know," Nick said, "Since I'm a sly fox, I might have read the hotel's ledger when I was leaning across that desk. And I might have seen that there was a Thomas Logan in room 14 on the first floor paid up from August twenty-fifth through the end of September. And if you were a sly bunny..."

Judy's ears perked. The hotel room key was numbered 114, and it seemed like Thomas Logan could easily be an alias for Thomas Carajou. It wasn't as though they really needed to confirm from the hotel clerk that the mammal who had checked in was Carajou, as if they were in the right spot they had the room key. "And if I was a sly bunny, I'd remember that the clerk said to investigate all we wanted, as long as it wasn't in the lobby," Judy finished.

A broad smile crossed Nick's face. "Sounds like we have permission to me," he said.

Judy took a deep breath as she inserted the key into the lock, noting that the wood of the door around the keyhole was covered with old-looking scratches where mammals had missed in the past. She exhaled as the key turned smoothly in the lock, although it took her a fair amount of effort to get the door to open; it didn't quite fit properly in its frame, as it was ever-so-slightly lopsided with a gap that was about half-an-inch wide at its tallest where the door didn't meet the floor. The curtains of the room's lone window had been drawn and it was too dark for Judy to see anything until she reached in and found a light switch that turned on a feeble overhead bulb. "Fifty cents a day sure doesn't buy you much, does it?" Nick asked, and Judy nodded in agreement.

About the only thing Carajou's hotel room had going for it, compared to Judy's apartment, was that it hadn't burned down. It wasn't any larger, and since it didn't have a closet what little furniture there was made it seem all the more cramped. The veneer on the headboard of the narrow bed was peeling away, and the brownish color of the bedspread was speckled with plaster dust that had fallen from a large crack in the ceiling that had been inexpertly repaired. The only other furniture was a battered desk, a wobbly looking chair missing a spindle in the back, and a small set of drawers that closed crookedly. The walls had been sloppily painted white, with splashes here and there on the dark baseboard that ran along a scratched and scuffed floor of wooden planks that creaked and groaned under even Judy's weight. There wasn't a bathroom or a kitchen attached; the only door the hotel room had was the one that connected to the veranda that ran along the outside of the hotel.

Carajou didn't seem to have much of a concern about housekeeping or many possessions. The bed hadn't been made and was a rumpled mess with dirty clothes in a crumpled heap to the side, and there were empty cans of fish and vegetables in a pile near the desk. At the foot of the bed there was a suitcase and what looked like an over-sized (from a bunny perspective, at least) violin case. The desk had a few crumpled up wads of paper, a pen, and a hinged picture frame atop it, so Judy started there while Nick started going through Carajou's drawers.

Although Judy had intended to start with the pieces of paper, once she got to the desk she couldn't help herself; the pictures in the frame had caught her attention and she picked up the delicate hinged frame. There were two of them, one on each side. The one on the left showed a female wolverine, probably in her early twenties, wearing an elegant gown and playing a viola. Her eyes were closed and her lips were set in a kind of half-smile of concentration. The background of the picture was dim and out of focus, which made Judy think that the wolverine had been playing on a stage under a spotlight.

The other picture showed the same female wolverine seated at a table with a male wolverine who was only barely recognizable as Carajou. Judy had seen Carajou, both from across the room in the Thief of the Night and also his corpse in the medical examiner's storage drawer, to say nothing of the photographs she had seen as part of the Bureau of Prohibition's files. That Carajou was younger and didn't have any scars in the picture she was holding explained only a part of why she found him difficult to recognize. It was because he was smiling. Even that wasn't quite accurate; he had been caught in the photograph in the middle of what was obviously a roar of laughter, and while the image was somewhat grainy Judy thought that she saw tears in the corner of his eyes, he was laughing so hard. He was holding the female wolverine's paw in his, and she was clearly laughing too; although she had put her free paw somewhat demurely across her mouth it was obvious from her eyes that she found whatever was making Carajou laugh nearly as funny as he did.

The pair of wolverines were seated at a table covered in a white tablecloth that from the background looked as though it was in a mid-range restaurant. Neither Carajou nor the female wolverine were especially well dressed, as his suit looked somewhat poorly fitted and the female wolverine's dress looked as though it was missing a few of the beads that made up the pattern around the neckline. Still, they looked so incredibly happy together that it was hard for Judy to reconcile the image with the one she had formed of Carajou from what was in the Bureau files and what Nick had told her. The Carajou in the photograph didn't look dangerous or moody, and Judy held out the picture frame in Nick's direction. "Was Carajou married?" she asked.

Nick paused in the middle of his examination of the contents of Carajou's drawers, which from what the fox was currently holding in his paws looked as though they consisted mostly of unremarkable suits. "He was," Nick said, looking across the room at the little photograph, "She died years ago. TB, I think."

Judy nodded, glancing at the photograph again before setting it down. Nick had told her that he avoided talking to Carajou, and she couldn't imagine that the wolverine was inclined either to talk about his dead wife or appreciate mammals who did. Judy turned next to unfolding the wads of paper on the desk, but they didn't seem to have any particular value to the case. One of them was a grocery list that made it look as though Carajou mostly lived off of canned goods (which was believable considering the pile of cans next to the desk) and the other two seemed to be nothing more than scribbles or doodles without anything that looked like writing. Still, Judy carefully flattened the sheets and took them with her when she moved onto the suitcase and what must have been a viola case. The viola case was black, covered with scuffs and scratches, and was surprisingly heavy. When Judy flipped it over to look at the backside, she saw that a name had been neatly stenciled onto it. Faded white letters read "AMELIA CARAJOU," and Judy noticed that while the text seemed fairly old, the letters of the last name looked fresher. Examining it more closely, she saw that the part of the case under the word "CARAJOU" had been painted black, and the paint was starting to chip away.

In an instant, Judy thought that between the pictures and the viola case she understood Carajou's marriage. When he had met his wife, she had been a viola player. Maybe it had been in a club or a vaudeville show, but somehow they had connected and eventually married. Amelia had kept playing the viola, painting over her maiden name on her instrument's case and then adding her new last name. At some point—maybe ten years ago, maybe fifteen—she had died of tuberculosis, and whatever light there was in Carajou's life had been extinguished and he had spiraled downwards, becoming ever more violent and cruel, until his eventual death.

Maybe Carajou had always been a dangerous mammal and he had either hidden that side of himself from his wife, or maybe she knew but didn't care. Somehow, though, Judy didn't think so, which made it all the worse that he had died alone, unloved and un-mourned, with nothing to show for his life. Judy thought that there might be more mementos of Amelia in the viola case, but when she undid the latches and opened it what she found couldn't have been further from that.

The viola case's contents were the work Carajou had dedicated himself to, pure and simple. The reason the case had been so heavy became immediately apparent—there was a Gazelle submachine gun, broken down into its component parts with two drum magazines, a compact pistol, and a few boxes of ammunition. The interior of the case was covered with red velvet that had started to lose its fuzziness that had somehow been molded to fit everything perfectly to keep the items from moving.

At some time between when Judy had gone to the viola case and when she had opened it, Nick had searched the dirty laundry by the side of Carajou's bed with no apparent success as he stood up and gave a low whistle at the guns and ammo. "A Zootopia typewriter," Nick said, and then walked over to take a closer look, "That certainly fits Crazy's style."

"This might have been what Carajou used in the Tundra Town shooting!" Judy said, as the possibilities ran through her mind.

Nick nodded slowly, his tail waving from side to side as he thought it over. "So maybe Carajou, Scursly, and Bauson steal a Camellac from poor rich Mr. Vanderbeaver," Nick said slowly, "They do the job at Tundra Town Lanes, and then Lionheart starts cleaning up. Maybe he decides he doesn't need any of them anymore, so he has Scursly and Bauson kill Carajou and frame Medvedeva, and then he has Scursly and Bauson killed."

Nick had put into words what Judy had been thinking, and she nodded her agreement. "So how do we prove that?" Nick asked, spreading his paws apart.

"The police can compare bullets at the scene to one fired out of this gun," Judy said, remembering a brief article she had read on the forensics of bullets, "They could prove that this is the gun!"

Nick nodded, seeming impressed. "That's a good start," he said, "Now how about that suitcase?"

Although Judy could feel her heart beginning to race in excitement, she paused before opening it, looking down at the still somewhat crumpled pieces of paper she had left on the floor when she opened the viola case. "Do these look like anything to you?" she asked, giving him the papers.

Nick took the pages and looked at the top one thoughtfully for a long moment. "It... appears to be a grocery list," he said at last, "Was this a trick question?"

"Not that one," Judy said, gesturing to indicate that he should look at the next page.

He shuffled the pages and looked at the next one, frowning in concentration. He rotated the page first clockwise, and then counterclockwise, and then stopped. "This is Tundra Town, isn't it?" he said, and then he put the page down, "It's missing some roads and it's not drawn very well, but I think this is Tundra Town."

Judy looked at the page from the same perspective that Nick was, and while it still appeared to be nothing more than a random series of squiggles, she saw how it could be a poorly drawn map. "This one is too," Nick said, rotating the third page to show that the two series of lines were in more or less the same pattern.

"If you say so," Judy said, and her lack of confidence in her ability to see the map he had must have been evident in her tone, because Nick clucked his tongue and shook his head.

"We'll make a Zootopia native out of you yet," he said, a slight smile touching his features, "In no time you'll be complaining about taxes and how much better the city used to be."

"Maybe you can help me with those taxes," Judy said as she put her paws on the suitcase's latches.

Nick shrugged with an almost certainly feigned modesty. "I do have a bit of a talent with numbers," he said, "Now are you going to open that or what?"

The suitcase was made out of emu skin and was somewhat scuffed and battered, particularly where the lid met the rest of the case. It popped open without resistance, though, the spring-loaded latches coming clear. The suitcase itself was mostly empty except for a beat-up binder with a cardboard cover and some clothes that had been wrapped around it. Judy carefully lifted the binder out; it was more than an inch thick and fairly heavy. The cover wasn't labeled, so Judy flipped it open to the first page, which was a piece of paper blank except for a single typewritten word in the center: "CONTRACTS."

Judy looked up at Nick, who simply shrugged and motioned her to turn the page in a perfect mimicry of how she had gestured for him to flip through the pages that had been crumpled up on Carajou's desk. The next page was blank, but on the back of the page when Judy kept turning pages she saw what Carajou had written:

DATE: 04/06/24

JOB: Get vendors on Kugluktuk Street to leave or pay Big a cut.

CLIENT: Mr. Big

CONTRACT TYPE: Verbal

PAYMENT: $25

Nick looked up from the page and Judy, an expression of amazement across his face. "Carajou kept records?" he asked incredulously, "Crazy kept records?"

Judy was momentarily as dumbfounded as Nick was, and then kept flipping through the pages until reaching the second to last one. As she had flipped through the binder, Judy had noticed that in contrast to the format that Carajou had used, which didn't seem to change at all, he had occasionally included notes, seemingly on the occasions when a job had been given to him in writing. Some of those jobs had been written on envelopes or napkins or scrawled into the margins of yellowing newspapers, but she paid them barely any mind until she had flipped through the years to the last entry. The final entry was opposite a note written on a piece of bond paper in an elegant and perfectly legible script. The note was a single unsigned line: "Inquire about renting Tundra Town Lanes for a party of six to eight at 5PM."

Carajou's entry opposite the note read:

DATE: 09/28/27

JOB: Kill Koslov and his associates at Tundra Town Lanes tonight. 6 to 8 mammals expected present.

CLIENT: King Lionheart

CONTRACT TYPE: Written

PAYMENT: $5000

Judy looked at Nick, her eyes wide. "This is it, isn't it?" she asked, unable to keep the wonder out of her voice, and it seemed all Nick could do was nod.

Author's Notes:

Before any of my usual notes, I found something pretty cool that I think is worth sharing. The artist yelnatsdraws over on DeviantArt independently came up with the idea of doing Prohibition-era Zootopia characters and she made some amazing pieces worth checking out. I can't include direct links, but I definitely recommend checking it out! As they say, a picture's worth a thousand words, and no matter how well I try to describe something I don't think I could match how well yelnatsdraws has captured the spirit of 1920s fashion and applied it to Nick and Judy. I figured that if you like this story, you'd probably like her artwork too! And now, onto my regular notes.

After the Beatles broke up, George Harrison recorded a song in 1970 called "My Sweet Lord." It's a great song, but there was one slight problem with it—it used the same melody as song by the Chiffons from 1963 called "He's So Fine." In the inevitable lawsuit, it was decided that, while Harrison had not consciously copied the melody, since he was aware of "He's So Fine" it still counted as copyright infringement. This is probably one of the best know stories of cryptomnesia, or someone thinking that they've come up with something new and original because they've lost conscious awareness of what inspired their idea.

The reason that I bring this up is because I did not deliberately make Carajou a wolverine so that I could use the chapter title of "Wolverine Blues." With a couple exceptions, I determined chapter titles after the fact, trying to find something that worked. I did, however, research quite a bit of music from the 1920s before writing this story, and the title of the 1923 Jelly Roll Morton song must have stuck in my head somewhere. In any case, I think that the title works well for the insight that examining Carajou's hotel room gives into the sort of mammal that he was.

Polio has been known to occur for thousands of years, but it wasn't until the 20th century that there started to be epidemics of it. The reason for this is pretty counter-intuitive—in cities, the sanitation had gotten too good. It seems as though improved public sanitation should lessen the spread of diseases, and this is true overall. For polio, better sanitation meant that people were generally not exposed to it at a young age and did not develop immunity to the virus; this meant that when outbreaks did occur, people were at a greater risk of developing the paralyzing form.

Polio is extremely virulent, spreading most frequently from water contaminated with infected feces, but it can also spread orally. Paralysis from polio is actually pretty rare—only about 0.5% of all cases, with up to 70% of cases showing no symptoms—but from how contagious it is there were thousands of victims in the early part of the 20th century.

Although the polio vaccine wasn't developed until 1950, even in the earlier part of the 20th century scientists had a fair understanding of how the disease spread. For this reason, it was very common in areas with active outbreaks to shut down public swimming pools and is one of the reasons why many places in the US have a ban on spitting in public. It was also not unheard of for health departments to label buildings with quarantine placards when occupants had active polio infections and not allow anyone in or out.

I thought that it made sense that the Rainforest District, as an artificially warm and humid environment, would be at likely the greatest risk for polio outbreaks of any of Zootopia's districts. Indeed, while polio outbreaks tended to be the worst in the summer in places with temperate climates, there were essentially no seasonal differences in areas with tropical climates. I think it also makes thematic sense as an example of Zootopia failing to live up to Judy's expectations as what should be a lush and vivid area is instead full of withering and dying plants as a result of shutting down the climate control systems.

Of course, polio is really only a danger to humans, but for the purposes of this story I've made the assumption that it has the ability to jump species.

Fifty cents a night for a hotel room is relatively cheap by 1920s standards, although as Nick observed the hotel really didn't offer much. It was actually somewhat common in the 1920s for people to live in hotels, even poor people, as prices were effectively lower than they are now even when adjusted for inflation.

"Goof" was 1920s slang that could refer to either someone who was foolish or a boyfriend. Considering that the tapir started by quoting an hourly price for a hotel room, it was being used somewhat sarcastically.

Thomas Carajou's alias of Thomas Logan is naturally a reference to the famous Marvel Comics character of Wolverine, whose real name is Logan.

TB was a common name for tuberculosis in the 1920s, as by that time calling it consumption was somewhat old-fashioned. A vaccine for tuberculosis was first widely available in 1921, but it wasn't curable until the development of the antibiotic streptomycin in 1946. In either case, the pictures that Carajou has would be from between about 1900 and 1910, before those developments.

The Gazelle submachine gun found in Carajou's apartment is a reference to the Thompson submachine gun, the gun that probably immediately springs to mind when people think about gangsters in the 1920s. Calling it a Gazelle submachine gun is a reference to the species known as Thomson's gazelle, and is of no relation to the character Gazelle in this story. The Thompson submachine gun was invented in 1918 and didn't have much demand at first, as it was quite expensive, had very poor accuracy, and was heavy. However, its high rate of fire made it an effective weapon at close range, so for gangsters who could afford it the Thompson submachine gun became a weapon of choice. It also saw use in WWII, where it was prized for clearing trenches and for close street battles. The drum magazine is kind of iconic for the weapon, although a more standard-looking (though lower capacity) box magazine was also available. The Thompson submachine gun had many nicknames; beyond the common "Tommy Gun" it was also called a "Chicago Typewriter," hence the use of "Zootopia Typewriter."

Matching a bullet to a gun is possible with weapons that have rifled barrels (which is most modern firearms), as in the process of passing through the barrel the grooves carved into the barrel create a pattern of striations on the bullet that are unique to the gun that fired it. The use of this method was first documented in 1915, when microscopic examination of a bullet found at a crime scene was compared to one fired from the suspect's gun demonstrated that it could not have been used in the crime. The technique was refined with the invention of the comparison microscope in 1925, as it made the examination much easier. The inventor of the comparison microscope, Calvin Goddard, also played an instrumental role in the investigation of the St. Valentine's Day Massacre of 1929. The members of Al Capone's gang who committed the murders had disguised themselves as police officers while they committed the crime, and Goddard was able to use his microscope to conclusively prove that their weapons had been used and the police had not been involved. This also contributed to it becoming widely known that such a comparison was possible.

Obviously, 1929 is after this story is set, but I think that it's reasonable that as an aspiring police officer Judy would at least try to learn about forensic techniques, and it makes sense she would be aware that bullet comparison could be done in 1927.

Ring binders were invented in 1886, so they could definitely show up in the 1920s.

As always, thanks for reading! I'd love to know what you thought!