All this time to talk and explore, and about all you've managed to find with certainty is the lack of a way out. How were you even brought in, then?
But then there were the two doors you couldn't open—Jackalope's Room and Wardens' Room. You wouldn't be getting in the first regardless given the size of the door, but the other? Surely worth your attention.
And so the handful of you not discussing your crimes in the cell block are around when it finally opens.
First hops out a little antlered bunny who only pauses to regard you with a twitch of the nose before proceeding straight across the hallway. Jackalope, presumably. How exactly it had its own room you weren't sure, but it couldn't have been that normal a creature when it went about in full uniform. Not to mention the, uh, mythic species aspect.
But if any of you want to go cryptid hunting, now doesn't seem to be the time. The three humans in similar uniform seem much more pressing.
The smirking redheaded woman looks you down with a clear air of appraisal. The bespectacled man mutters to himself as if running through lines for a work presentation. The silver-haired person absently adjusts their sash as they survey each of your faces.

"Oh, here's a few we were expecting," the woman coos at last, tapping her chin. "I think this will be fun."

"Hopefully more... fulfilling than fun?" the person responds.

The man huffs. "More confusing than anything if we don't pass on any information." He peers at the poor excuse for a crowd with a frown. "Let's gather in the main hall. All of the prisoners, preferably."
The other wardens don't object, and with the suggestion of actual information, it's hard for you to, either. Once the summons is passed along, the gaggle of prisoners finds itself in the hall, some a bit closer to each other and some much farther away (and some, perhaps, just out into the hallway for the sake of not meeting where they were ordered). While you're not likely to stay quiet for whatever announcement is about to be made, you can at least stand to hear what they say before you take real action. The wardens, murmuring among themselves until you've all assembled, finally get arranged in somewhat of a straight line at the top of the stairs, then face you again.

"First things first," the man begins. "As the room nameplate suggested, we three are the wardens. You thirteen are the prisoners. Here in the MILGRAM, we hold absolute authority over you."

"Not that we plan to use it harshly!" the person cuts in, waving their hands. "Just enough for... some sort of order, really. We'll try to be fair, since that's the whole point. Ah, and you can call me Sie, by the way. Whichever pronouns."

The woman seems to see this as her chance to step in. "And I'm Bea, though I'm not averse to a good nickname if the muse takes you."

The man sighs, adjusting his glasses (apparently just for the glare since they seemed to be sitting perfectly well already). "Ei. So, as I was saying. You are all prisoners in a special prison. We already know each of you is a murderer, but we don't know the story behind it. You're free to give us your own take on what happened, but we can't expect every one of you to be truthful about it."

"Yes, where would be the fun in that?" Bea says. "We'll also get to view your subconsciouses more directly through one of MILGRAM's lovely features—called projections. It's a very simple process by the sound of it. You'll just take a seat, and we'll be off to explore!"

Sie nods. "It should be similar to an immersive hologram, I think. And while only we wardens will be passing judgments based on what we find there, I don't think there's any reason some more of you couldn't come along. If, ah, maybe you'd like to share your projection with your friends? If you... make friends here."

At that, Ei gives them an incredulous look but quickly turns back to the rest of you. "As Sie said, we'll also be passing judgment on your crimes. You'll each have three trials, and at the end of each trial we'll decide if each of you is forgiven of the murder or unforgiven." Then, muttered, "Those being the only two options."

"But we can use whatever standards we like!" Bea says. "This isn't any legal red-tape sort of investigation. We just decide your verdict based on how we feel about you at that point."

"More or less?" Sie rubs their arm. "But... yes. That's the long and short of it, I think. MILGRAM needs a bit of time between projections, it seems like, so in the meantime all of you will eat and sleep here and such. If there's anything within reason we can do to help make it more livable, let us know."

"Within reason," Ei repeats. "Make any request you want, but we're under no obligation to carry them out. We make the rules here, remember."

Bea raises an eyebrow. "You've said so, yes."

"And that's... most of what we know, really," Sie says. "There will be consequences to your judgments, so... we'll do our best to judge well. Thank you."

"What is this, public broadcasting?" Ei sighs. "Just stay in line, and we shouldn't have any problems."

"Or if you do step out of line, at least make it interesting!" Bea winks.
These were your new authorities, huh? It's hard to know what to think—subconscious delving? Consequences your wardens don't even know? And aren't some of you speaking different languages, despite understanding perfectly fine? What is going on in this place?
You suppose you'll just have to work out what you can. Maybe viewing some of these "projections" could help?
Or maybe you're just trapped in some inexplicable underworld you're doomed to never understand.
Whatever your opinion, you don't have much option but to make yourselves comfortable.