They're allowed to go in with a warrant whether or not you're there to allow it. But I understand you have access to places they physically can't reach without your cooperation. And yes, your obligations don't attach until you've been officially informed. The practical effect is that if you think disappearing isn't too extreme, you wouldn't be doing anything illegal.

Do they have to physically reach me? What if I relocate my principal mortal world presence to Brazil and they send me an email?

Federal authorities could cooperate with the nation you relocate to, and have them contact you in person. They'd do that if it were about stopping the Nine. As it stands, they're probably content enough not to make much effort as long as the Nine are no longer a problem and you aren't around to conspicuously not help.

Okay. Is there a good way to negotiate my conditional handing them over without running afoul of an insistence on an unconditional such surrender?

There's no procedure set up for that. It isn't a situation that comes up often, and there's no single person making most of the decisions. I could try negotiating it, if you send me a list of your conditions.

Choosing Earths at random means many of them are too different along a lot of axes. Climate differences are to be expected, but one world has less gravity and no atmosphere to speak of, another appears barren but usable unless she tries stepping through in which case it becomes impossible to breathe, a third gate fails due to the lack of anything resembling an Earth. Eventually one of the gates leads to a world similar to Earth Bet without the humans.

An update from Quinn: most of the people involved are very much in favor of prosecuting any of these (apparently it's a boon to their careers) and they're willing to make some concessions. No collar preventing the singing supervillain from opening her mouth, for instance, and more importantly they won't be trying for capital punishment. (The fact that the Siberian is effectively unkillable may or may not be part of the reason for this.) But the Birdcage is a sticking point; some of his counterparts are of the opinion that if the Slaughterhouse Nine don't get sent there then there is no reason for it to exist.

Then maybe there isn't a reason for it to exist, Promise comments. Does not trying for capital punishment mean not getting it?

Yes. The jury can't decide on their own to execute someone.

How flagrantly illegal would it be to leave the Siberian with permission to pick up her friends and leave if someone did try for capital punishment?

Flagrantly. At most, the remedy would be to challenge the ruling in court before the scheduled date, and get a bigger judge to overrule it. No need for any new felonies at all.

I am deeply dubious about this entire process. But assuming for the moment that I trust those involved not to seek capital punishment and I'm satisfied that these particular individuals can probably be considered capable of comfortably inhabiting the Birdcage and therefore are not cases of my specific problem at work, what's my next step?

If you decide to trust it, you can just send them to the nearest PRT office. You will almost certainly be asked to testify about capturing them, but the the system isn't meant to rely on continued involvement of whoever caught the defendant.

Is it reasonably guaranteed that someone who has registered a willingness not to seek capital punishment will be prosecuting?

Reasonably. It won't be legally enforceable until the agreement gets made on their behalf instead of yours, but I'm as confident as is possible outside that constraint.

Who gets to make agreements on their behalf?

Their lawyer. It can't be me since you're involved and I'm representing you, but a deal that involves not being executed is what any defense lawyer would aim for. Under the circumstances.

Do I get to talk and/or help select their defense lawyer? I have been getting the impression that even champions of the ostensible principles of the mortal justice system might be pleased to see these particular defendants suffer.

The Siberian doesn't talk, is that a problem?

It will make things more complicated, but if she can understand what's going on and express preferences to her defense team then being mute won't by itself be prohibitive.

Subject to the same caveat that I don't have unlimited influence, yes. For something this high-profile there's even less of a guarantee of keeping them out of the Birdcage, but I'll do what I can.