Ok so I’ve been thinking about this for a while about Elias’s imprisonment.... So generally when people are accused of a crime they get a trial. and it must be proved beyond a reasonable doubt that the accused is guilty. Now: the only evidence that they had was the tape where Elias admitted to the murder of Gertrude and Lietner and possibly the tape where he actually killed Lietner? Unsure on that one. Yes both of those tapes could be prettyyyy damning evidence but you can’t really find someone guilty on just that. Elias could deny it was him on the tape or it was altered and I have a hard time believing he could actually be charged on both their murders based on tape recordings. Obviously AI voice wasn’t like it is today back in good ol’ 2017 but it probably wasn’t far off and I’m sure the defense could claim that the tapes were digitally altered. (You can make an audio file and record it onto a tape recorder pretty easily). So here are my theories:

1. Elias threw the trial and just admitted guilt. He wanted to go to prison anyway to get out of having to be around Jon and to instill Peter at the Institute. However, I think this is the least likely scenario since it’d be more difficult to get out of should anything go wrong (aka if Jon actually decided to die and he had to go to a backup plan). He probably also wouldn’t want to ruin his reputation by being found guilty. Sure being accused of murder isn’t a great look either but... lol

2. The trial keeps getting delayed due to bureaucracy/Elias’s meddling and while he’s awaiting trial they decided he was possibly too dangerous to be free. I did look it up and you can be imprisoned before trial in the UK if its determined to be necessary.

It’s possible that he organized something through blackmail to allow his court date to keep getting postponed. Also he could simply have organized with the police to simply hide out in prison without any charges (this is kinda like... a fourth theory but it wasn’t too different from the second so i didn’t make a whole new bullet point). The whole thing just for show. He literally didn’t need to be in handcuffs he’s just being dramatic

3. There *was* more evidence.

“All the evidence” does imply more than just the tapes. Perhaps they had fingerprints they could match on the pipe. Again with the tapes, Elias could argue they were spoofed and refuse to sign any confession. He also already is able of producing counter evidence through manipulating the cameras in the Institute. Fingerprints would be harder to dismiss but then... Jon’s fingerprints would also be on the pipe.

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Anyway in my person theory number 2 is the most likely scenario. In MAG 122 we get this line from Basira:

Notably she doesn’t say he was convicted or charged. So if theory 2 is correct he really could just leave anytime he decides/speed through his trial and be found innocent should anything go awry. I find it interesting to speculate on how many backup plans Elias had going at once. Obviously all the marks were meticulously planned out, but even the best laid plans fail sometimes. It doesn’t make sense for him to allow himself to be proven guilty when Jon could kick the bucket and then he’d be stuck in prison delaying his ritual.

... Ultimately none of this really matters to the plot of the show I just thought it was interesting.