Less than an hour later, Katherine and Elizabeth entered the interrogation room at BPD, where Jonah Welch was writhing in his chair. He would have been climbing the walls by now if he hadn't been handcuffed to the table.

"What do I have to do to make you believe me?" he pleaded. "I swear on my parents' grave, I didn't do it."

Elizabeth stepped right up to him and looked down at his flushed face. The prisoner winced, beads of sweat running down his forehead. For a moment he seemed to think the detective was going to hit him. But instead, Elizabeth pulled a small key from her pants pocket and uncuffed him. That startled Welch even more.

"What's the matter?" he asked fearfully.

"You're no longer considered a suspect in this case," Elizabeth assured him, hooking the handcuffs on her belt.

Welch just sat there at first, unable to believe her. Then he looked up at Elizabeth and became angry. "Are you kidding? Was this all just a big mistake, or what?"

"Yes, and it was our mistake, Mr. Welch," Katherine replied in a calm tone. "But someone wanted us to commit it."

Welch stood up indignantly. "What do you mean by that now?"

"It was just like you said. You got double-crossed," the detective explained, stepping in Welch's way as a precaution. She could feel the man's hot breath, which smelled like sauerkraut.

Welch simply sank back into the chair like a frightened child. "Double-crossed? Why? By who?"

"That's exactly why we need your help, genius," Elizabeth replied.

Katherine, treating him like the victim he now was, pulled up a chair and sat down across from the man. "I know you said you couldn't think of anyone who could do something like that to you," she said sympathetically with a slight frown. "But you really have to try, we need your help. Who could possibly want to hurt you?"

"I have no idea," the man replied in a shaky voice.

Elizabeth sat down in the remaining chair and struck a more empathetic tone. "Look, my friend. Whoever this guy is, he's cunning. So far, he's had his fun by playing us for fools. But no one comes up with such an elaborate plan when he doesn't want to see the victim, you, hanged."

"Please understand," Katherine continued, "Detective Rizzoli and I are not trying to trick you somehow. She arrested you because there was solid circumstantial evidence. And so the person who killed all those women and laid those tracks may not leave it at that."

"What ... what do you mean by that?" asked Welch, not seeming sure he wanted to hear the answer.

"We're taking you into protective custody," Elizabeth explained with furrowed brows. "Remember, this guy has it in for you. When he finds out that it didn't work, that we didn't fall for his misdirection, he'll try to get you out of the way in other ways."

Now Welch sat frozen in fear. "You're not going to let him do that, are you?"

"We'll put you up in a nice hotel and have you protected 24/7. At the city's expense."

He relaxed just slightly. "Doesn't sound so bad," he said hesitantly.

"It's better than your apartment in Jamaica Plain, and it's certainly better than fifteen years in Suffolk County Jail. But it's still a prison. Until we find this guy and bring him down."

Welch buried his face in his hands as if there was no way he could win. "I want to help you guys, I really do. But for the life of me, I don't see how."

"Just think," Katherine said. "Make an effort."

"Who could want to see you in the electric chair?" the detective asked. "Did someone threaten you in the courtroom after your trial? Maybe a relative of your victim. Or someone you did time with?"

"I ... I don't know," Welch stammered, confused. The detective could almost see him struggling to remember all the arguments he'd had, all the people he'd turned against himself. She actually felt sorry for him. Welch turned to the doctor. "Does that mean I can go?" he asked.

Elizabeth exchanged a quick glance with her sister. "That's up to Detective Rizzoli," she replied.

"In theory, yes," Elizabeth sighed, leaning back in her chair. "But as soon as you leave the building, you become a live target." Welch didn't know that Elizabeth was making sure the man wasn't playing with them. There was still the vague possibility that Welch knew the killer and was protecting him. "Just hold still a little bit, Jonah. Keep thinking. We'll leave the handcuffs off and one of my colleagues will get you something to eat. As soon as I get back, we'll put you up at the hotel. But first I have one more thing to check."

"And what the hell is that?"

"Your car," Elizabeth explained, raising her eyebrows a little. "You said earlier you hadn't driven it in weeks. We need to make sure you're telling the truth. The sooner you allow me to search the car, the sooner you'll be out of here."

Welch didn't hesitate for a second. "If you have something I can sign, give it to me."

Elizabeth nodded slowly. "Very well. You didn't hide the damn car, did you? Because we had people looking for it all night, but couldn't find it."

The detective had finally asked a question Welch could answer. "There's a gas station about fifteen minutes south of here. I pay the owner every month to let me park my car there."

The detective and the doctor now stood up and left the interrogation room.

Elizabeth took her phone and informed Jane that she had found out where the Crown Vic was located and she would take a look at the car on site before lifting her gaze. "It might take me an hour or two. Um, we have free cots in the bedder if you want to lay down for a bit, or you can go to my place, the girls are already in school and you'll have some time for yourself." She set off and then paused, saying with furrowed brows. "I would recommend you go to my place. It doesn't smell like old stinky socks."

Katherine chuckled briefly but then became serious again. "I'll go with you. I need a coffee and something resembling breakfast anyway."

Elizabeth took a long look at her little one and nodded slowly. "All right, come on."

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It took the detective less than fifteen minutes to get to the 'gas station' in question, a run-down old shack where, in truth, no gasoline had been sold for decades. But Elizabeth left nothing to chance. She had asked a friend to drive over, confirm the car was there, and watch it until she arrived. She asked Forensics to show up in a civilian vehicle so they wouldn't draw attention. She also explicitly ordered that no one was to touch the car until she was on the scene.

Upon their arrival, it was clear that Elizabeth's requests had been heeded. The uniformed man waved from the driver's seat of his patrol car and drove away, while Elizabeth and Katherine got out and Aitken from Forensics approached from the side.

"Thanks for keeping it low-key," Elizabeth said of forgoing the yellow police tape.

"I figured if I'm going to use a camouflaged vehicle -" Aitken replied, gesturing to the ratty old Chevy she had come in. "Your perp's ride is a thousand times better than mine."

"So the car has been here the whole time?" asked Elizabeth. Aitken led her to the other side of the gas station building.

"Yes, but I can see why the patrolmen didn't spot it. I almost didn't find it myself when I got here," Aitken replied with a frown. "But see for yourself."

They passed through the garage door, and then the other two women understood. Six battered vehicles stood there, two in a row, next to the building. Only a closer look revealed Welch's black Crown Vic, squeezed between a fence and a rusty '60s bread truck.

"I asked the guy who owns the place," Aitken said now. "He parked the bread truck here a week and a half ago and hasn't moved it since."

"I could have told that just from the dirt," Elizabeth muttered with a frown. "Why don't you take some pictures before we crawl in there?"

Aitken nodded and moved away as a silver-haired man in his fifties approached them, wearing a mechanic's overalls. He parked the two vehicles next to the bread truck and Welch's Ford.

"No question about it," Katherine remarked, finally getting a look at the Crown Vic's dusted tires. "This car was nowhere."

"Do you have the keys?" asked Elizabeth.

Aitken nodded and held them up. "Do we have a warrant?"

"Much better," the detective replied with a wry smile. "A written authorization from the owner."

Aitken was unhesitating in handing her the keys.

Elizabeth put on gloves, opened the driver's side door of the Ford, and took a peek inside. The interior of the car was worn but remarkably clean.

Aitken opened the driver's side rear door and inspected the back seat. "I'll have the car taken to the lab so I can Luma-Light it for blood," she said, "but I don't see or smell anything that would indicate there was a body in here."

"We haven't opened the trunk yet," she reminded Elizabeth, operating the release mechanism inside the car before moving to the back. "Just as clean as the interior," she sighed.

"If there had been a body in here, we'd notice."

"I don't smell ammonia or cleaning solution either," the detective noted, pushing the trunk lid closed and exchanging a glance with her sister, but then Elizabeth paused. "Aitken, do you have a magnifying glass in your magic box?"

"What's up, Sherlock?" asked Katherine, who was standing behind them.

"Sure," Aitken said, frowning as the detective pointed to the license plate. A few seconds later, the forensics officer looked up. "Fresh tracks around the bolts. You're right."

Katherine looked at the two of them, puzzled. "Right about what?"

Elizabeth took a step back to give Aitken room to work, then turned to her sister. "When we suspect a car has been stolen, the first thing we do is check to see if the license plates have been changed. You check to see if the plates are cleaner or dirtier than the rest of the car if the screws are shiny if there are fresh marks from a screwdriver on them or on the license plate."

Katherine looked at her big sister, almost fascinated, and nodded as she understood. "So you're saying that instead of taking the car itself, Rosa's killer stole Jonah Welch's license plates?"

"That's exactly what the detective is saying," Aitken confirmed. "But I've never seen anyone do that here."

"What?"

"He used Magic Markers in the same colors as the license plates and the screws to hide the marks he left when he mounted and dismounted them," Elizabeth replied with furrowed brows. "He even smeared dirt on it to conceal everything."

"But it still didn't quite work," Aitken replied, smiling broadly.

"We'll find he did the same thing on the front," the detective nodded in agreement. "And that will also explain why the camera at the toll booth picked up Welch's license plate number."

Katherine was still confused. "But that would mean -"

"Right," agreed her sister, who was also amazed. "This guy really had it out for Jonah Welch in a massive way. He wanted to frame him so badly that he bought his own '98 Crown Vic, the same color as Welch's, same model and the same type of tire, and to tighten the noose, he put Welch's license plate on it."

"And when he was done, he switched them back," Aitken added. "Both times probably at night, the bread truck gave him the cover he needed. No one could see him."

Elizabeth took a long look at the forensic scientist and frowned deeply. "Let's tow the car to your garage. Go through it top to bottom. Maybe our wise guy did leave something behind."

"I doubt it," Katherine objected, and the other two women looked at her in amazement.

"Everyone makes mistakes," the detective almost growled. "Even our real culprit. It's pretty much impossible not to leave traces, like brushing against a seat or accidentally coughing."

"This guy doesn't make mistakes," Katherine insisted. "You won't find anything else here, just as you won't find the real car the killer used to transport Rosa's body in truth. In fact, you won't even discover a trace of that car or find out where he bought the tires."

Elizabeth grunted in amazement and tucked her chin, lowering her brows all à Jane. "How in the world can you know that?"

"Because I'm beginning to understand who we're dealing with," Katherine replied, clasping her chin briefly and thoughtfully. "He's organized, meticulous to the point of obsessiveness because he thinks he can defeat you. Defeat us. He thinks he's smarter than all of us. The question is, what made him become active after so many years?"

"I have another question," Aitken interjected. "Usually when someone thinks he's smarter than the police, he wants to rub it in, he wants us to know that he is. So why is this lunatic trying to pin Rosa Castillo's murder on this Welch guy?"

Katherine opened and closed her mouth again, Aitken's objection making sense. "You know, we haven't considered the possibility that Welch isn't just an innocent poor fool after all, and the killer's real goal is to make us look incompetent because we're locking up the wrong person."

"No. I mean, sure, that's kind of the point, too. But he wants to keep this cake and eat it at the same time," Elizabeth said, unconvinced. "There's got to be something. Some connection between Welch and the real killer. We have to look."

"You can do that, but I bet it will be a waste of time," the doctor said.

"That's police work," Elizabeth replied, not understanding the negative attitude. "That's what it consists of. We follow up on leads. We investigate all possibilities. It's never a waste of time if the wrong trail ends up leading to the right place."

Aitken watched the two women and concluded that this kind of conversation was already old.

"Yes, and the person who is playing with us here knows that and wants to see us run in circles," Katherine countered, unable to explain why her sister was so touchy all of a sudden, but not holding back her sharper tone.

Elizabeth could tell her sister wasn't comfortable taking out her frustrations on her, so she closed her eyes briefly and took a deep breath. "All right," she relented. "What about a connection between Rosa and her killer?"

The doctor shook her head. "That contradicts what I observed out the window. If there was a connection between Rosa and the man who led her away, there would have been some kind of familiarity. But my impression was that she had never seen him before."

Elizabeth looked at her little sister with a piercing gaze and her chewing muscles twitched, a sign that she was pulling herself together to keep from breaking out into an open argument with Katherine. "We need to talk to Rosa's mother again," she said as calmly as she could.

Katherine looked at the detective in amazement. "Why?"

"Because we didn't ask her if anyone was around the time of Rosa's disappearance to check on her," Elizabeth growled, her eyes hard.

Katherine held the piercing stare that normally would have intimidated anyone else. "Let me go there. Alone."

Aitken pressed her lips together and decided to back away slowly, letting the two women sort out the simmering conflict between them.

Elizabeth snorted briefly and shifted her weight from one foot to the other. "Why?"

"She's fragile," Katherine replied, starting toward her sister's car. "I don't want to scare her, and we still have to trust her to keep Rosa's death to herself."

"All the more reason why we should both drive," the detective explained, following her sister and already looking piqued again. "And just in case you forgot or didn't notice, I'm perfectly capable of being compassionate to the relatives of my victims."

Katherine stopped and looked at the older woman urgently, now the exact image of Maura, and just as stubborn. "I don't think that's a good idea," she said a little more emphatically.

"This is BPD business."

"Rosa was my patient."

"And now she's my victim," Elizabeth barked as she opened the driver's door of her car and slammed it shut again without warning. "We drive together, or I drive alone. The choice is yours, Kate!"

Katherine looked her sister in the eye and briefly toyed with the idea of going behind Elizabeth's back to Maria. But that would only cause the two of them to argue again, and she suddenly realized that she felt more uncomfortable than ever arguing with her big sister. She didn't want to be left out of the search for Rosa's killer. And she knew that this time the consequences would be more devastating if she went off on her own to investigate the truth and things got out of her control. She snorted in annoyance and rolled her eyes. "All right, then. We'll do it your way," she finally relented and sat down in the passenger seat.

"Thanks," the detective replied with a triumphant smile before getting behind the wheel of her car.

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Jane was sitting at her desk reading one of the many police reports and eating the sandwich she had ordered when someone suddenly opened her office door without knocking. The captain got ready to explain to this brazen subordinate that he or she had to knock first before they were allowed to enter. She straightened up and dropped the sandwich as Maura set her briefcase down on one of the worn chairs in front of her desk and looked at her wife, the captain, long and hard without saying a word, but she put one hand on her hip.

Jane waited for the lawyer to say something, then looked at her computer monitor only to see that it was lunchtime. She instantly wondered if she had forgotten that Maura and she were supposed to have lunch together that day and frowned a little. "Please don't tell me I forgot we had a lunch date and I forgot. I'm sorry, but as you can see -"

"Have you lost your mind?", asked Maura in a tone that would make even an Eskimo shiver.

" - I've got my hands full," Jane finished her sentence caught off guard, her eyebrows drawing together as she realized her wife's question. "Excuse me?"

Maura took a deep breath to keep her anger in check. "You're letting Liz and Kate work together on the Rosa Castillo case? What are you thinking?"

Jane tossed a paper napkin into the trash can under her desk, knowing this was going to be a conversation that consisted of personal and professional. "I think I'm exhausting all possibilities to solve this case. Liz is my best investigator -"

"Who you benched, and who hasn't done much more than desk work for more than a year," the prosecutor interrupted the captain.

Jane decided to pay no further attention to this objection. "And Kate is an outstanding forensic psychiatrist -"

"Who is personally involved in this case, since the victim Rosa Castillo was her patient," Maura interrupted her wife again.

Jane lowered her brows and exhaled slowly. "Who can get inside the head of a criminal better than any of us," she finished unusually calmly, an indication that she had to force herself not to hit the ceiling immediately. "How do you know about this, anyway? And wasn't it you who accused me of treating Liz unfairly?"

"I wasn't suggesting that you should make sure Liz commits professional suicide!"

"You think I don't know what's actually at stake here?" barked Jane suddenly, and Maura tucked her chin in surprise as the captain nearly jumped out of the desk chair. "I can think of a really much nicer place to start, but unfortunately we don't have that." She furrowed her brows and stepped closer to her wife. "Don't you think it's perfectly clear to me that both of our daughters will commit professional suicide if all this shit goes down the drain and the killer gets away?" She paused and tucked her chin as she realized that she had never mentioned that her daughters were working together on this case, knowing full well that Maura would freak out just like she did at that moment. "Who actually told you that Kate and Liz are working together on this case?"

Maura snorted, rolling her eyes and dropping her hand, which had been almost reproachfully on her hip the whole time. "That doesn't matter at all right now."

Jane narrowed her eyes and took a step toward her wife. "Yes. Yes, it does, because only a handful of select investigators from homicide, forensics, and the forensics lab are working on it, which leads me to conclude that there's a leak somewhere."

Maura looked at the captain for a long time and licked her lips, almost making it seem like she was looking for a good answer. She licked her lips again and lifted her chin a little. "Has it even occurred to you during all this time, while you've been working on this elaborate investigative process, to involve the D.A's office?"

Jane paused, considered for a moment, then furrowed her brows. "Well ... no, not exactly -"

Maura nodded slowly and slowly crossed her arms in front of her chest. "So you're telling me that you got my people involved, but you bypassed me, the Attorney General of Massachusetts?"

The captain suddenly felt as if she were being cross-examined and blinked with an unusual frequency. Even back when she and Maura had first met, this kind of skirmish had occurred, usually resulting in flirtation and ultimately a relationship that had produced their marriage and children, but for some reason, Jane felt at that moment like she was being accused of treason. "What your people do in your office, and what they withhold from you and what they don't, that's not my problem," she replied, regretting that statement as her wife's face hardened. "I was just doing what I thought was the right thing, Maura."

"The right thing," the lawyer laughed incredulously.

Jane dropped her shoulders and looked at her long and piercingly, dropping all her defenses. "Yes." She lowered her head as she walked to the office door and called into the bullpen that she did not want to be disturbed for the next hour and would not be taking any phone calls before locking the door and lowering the blinds. She leaned against the door and stared at the floor in front of her, running her thumb over her lower lip in thought.

Maura knew that expression more than too well and sat down on the worn brown leather couch that sat in the corner, frowning and waiting patiently for her wife to be ready to break the bad news.

Jane sighed loudly and sat down next to the blonde, propping her elbows on her thighs. "I don't know, Maura ... I think I blew the case twenty years ago. We separated, arguing about where the girls should live, then Liz and Kate were in constant competition over who was the favorite, and all I was concerned with during that time was making your life as miserable as possible." She paused and shook her head with her lips pressed together while Maura just listened. "And then you disappeared." She sniffled and looked at her wife for a moment, shaking her head.

Maura could see exactly that the frown was an indication that Jane was silently self-reproaching herself and rubbed her wife's back. "So much has happened in that time, Jane. All of our lives had been turned upside down."

Jane straightened up again and leaned back into the couch with a deep and loud sigh, running her fingers thoughtfully along her lower lip. "I don't know, Maura. There was nothing more important to me at that time than getting you home alive. Everything else ... had to take a back seat. If I missed something in this case because I wasn't focused on the case and the guy got away because of me, then -"

"No," Maura interrupted her wife harshly, and Jane looked at her with wide eyes in surprise. "No, you're not going to sit here and melt into self-pity over something that happened twenty years ago. You weren't the only Homicide detective in BPD during that time. So much happened twenty years ago, you don't have to blame yourself, Jane."

Jane looked at her for a long time and could see that the lawyer meant every word exactly as she said them and nodded with a sigh, yet she had the nagging feeling that she was to blame for the monster still roaming free through Boston, murdering more women.