They were indeed people traffickers. And they indeed offloaded military aged males into the target structure as cap had suspected they would. Shield, more specifically fury, had already cleared cap to engage and destroy these domestic threats as needed.
Cap continued to use the scope of his rifle to get the visual intel he needed before conducting any manner of physical op. He would try to kill as many of them as he could. The more damage he could do the better for everyone it would be.
He then saw them unload weapons. Probably for sale and for baddie use he thought. They would be used to cause chaos and destruction throughout the city to further weaken it and make it more ripe for a criminal takeover.
Intel had also warned of a rising global terrorist group known as the flag smashers. Obviously their implicit goal was to end the nation state. Obviously cap didn't care about nation states anymore but their actions did affect freedom. And all things freedom was his terrain. Whether or not these flag smashers were related to the cartels and other crime groups here was another matter altogether. But that was all part of his intel mission here.
He chose not to engage them in a sniper role but rather to infiltrate them instead. The intel value of this potential target was higher than expected. Steve could see that now and adjusted accordingly.
Standing cap changed his shield issue multifunctional rifle into the assault configuration before them slinging it. He was also armed with a katana and a number of other weapons for field use.
This changed mission profile would now require a different approach entirely. Up close and personal sort of thing. He set his rappelling anchor into the rooftop edge and swiftly went down. When down he recalled the shield issue field device and secured it. Staying in the shadows cap moved out and closer to the baddie target.
He pulled out a folding knife for what he had to do next. The target was inside a walled compound. Easy enough for an enhanced to overcome. In fact it took cap less time to get over the wall unassisted then to think about it. He was down and in the shadows again.
The first cartel sentry was closing in. Cap had timed this just right. He waited in the shadows for him to go by; then acted. Cap used the blade for this baddie's throat well enough and dragged him back into the shadows for disposal.
Cap moved in. He took down a few more sentries in a similar manner. Soon enough the target's exterior was open to him. He'd evaded the surveillance as well. Plus he had shield jamming tech on him. This combination gave him the edge he needed to do his job here.
He reached a side door access point and picked the lock. He could have forcibly breached it via body alone but it would've sounded the alarm. Cap wanted to keep stealth and surprise for as long as possible.
How he would deal with all the parties would vary depending on what he encountered here. All guilty parties would ideally be summarily disposed of. He intended to save the taxpayers' money wherever possible. And quite a lot of money could be saved here no doubt if cap acted as needed.
He stayed low and in the building shadows. He heard the cartel players yelling at their captives and slaves. Cap came to a corner crouched and spotted a group of them giving orders. This would be as good a place as any to do the misdeed.
Cap pulled out his katana and moved out. He then poured on the super soldier speed. The superhuman black operative and first avenger was at the cartel hitters before they saw it coming. And by the time they did it didn't matter. Cap being superhuman didn't need training. With his enhancements he was essentially a master swordsman by default.
His blade cut into them like a samurai of old; although cap was equivalently a ronin comparatively speaking. Something Bucky and Logan would understand well enough.
He showed them no mercy. Their guns came around and fired but cap's legendary tactical sense came through. He adjusted his tactics constantly and at a rate of speed that they could not adjust to. He moved almost like a blur. It wasn't as fast as Spider-Man or others but much faster than any peak human could counter.
The captives were stunned by this rough looking bearded man that had come out of nowhere and hit these baddies with such ruthless intent. Moreover, even though many of them knew who Captain America was in general they did not associate this man with him at all. And this was despite cap being right in front of them the whole time.
In little time that baddie group was cut down and gone. Cap returned to the shadows like a ninja. More alerted baddies came in to find their associates in pieces. They cursed and sounded the alarm.
Cap wasn't worried about it. He was satisfied with getting this far into a heavily guarded enemy base without getting detected. It didn't always go down this way. This good.
The enemy now searched for him. They also called in reinforcements. Cap could have jammed their calls but didn't. He was literally rolling with this whole thing and his enhanced gut told him to keep rolling with it.
He stayed in the shadows and remained empty handed for now. He then spotted a tech room. He snuck inside and killed the cartel baddie on watch there. Cap then took the seat and hacked into the system. Mentally enhanced he was able to break through the firewalls soon enough. He then had access to the cartel database. He sent the data straight to shield. It was a goldmine of intel. Fury would love it.
Cap logged out and returned to the shadows. His job here wasn't over yet. There were still people to free too. And liberation was what he was all about; be it occupied nations death camps or crime infested areas. All required liberation. And cap was still their guy.