The DEO is a major protagonist faction on Supergirl. Over the course of the show, the DEO has detained many people from various groups, seemingly with little indication of what rights, if any, their detainees have. Clearly, they are not police, but they are an official and (as of recent years) seemingly officially acknowledged federal law enforcement agency.
To be specific, they've arrested humans who are US legal residents or citizens (Maxwell Lord, Mercy and her brother), aliens who are US legal residents or citizens (which should be almost all of them since Season 2, thanks to the Alien Amnesty Act), and aliens who are not US citizens. Presumably, in theory, they might end up detaining humans who are not US legal residents or citizens, but I can't think of any examples.
To what extent do these prisoners have the usual legal rights of prisoners in the US? For instance, do the DEO prisoners have a right to trial? To attorney? Does this depend on whether they're human or alien; on whether they're a legal resident, citizen, or neither; and is it affected by the Alien Amnesty Act?