If it's someone we know, Bo Katan, the forger, or the big guy with the machine gun would be the only 3 suspects since they are the only 3 that have any kind of identity. And forger and big guy are kind of a packaged item in that regard. So it's either one or the other, or someone else we havent met yet.
This jailbreak was done before the events of this season. So motives may have changed between now and then. But if it had to be someone we know, my money is on the forger/big guy.