One of the co-defendends in the group chat starting taking screen shots when the writing was on the wall, I believe that is what I read earlier
The threat model guides say it many times, but its easy to forget, even if signal works perfectly the people your talking to can compromise you... by taking screen shots, using a second phone to take photos of the first phone, hooking up a audio recorder to record voice conversations, etc.
We also saw this behavior in some of the political trials post trump. Signal + screenshots.