Yeah, I'm operating off the idea in the OP that either the original DM or the group as a whole found this a problem that needed fixing. This will depend on the group for sure, and as this thread shows, many folks have strong feelings about this kind of stuff.
Personally, I don't have a problem with the PCs being anti-heroes or even villains, as long as things don't get creepy or whatever. Not a problem in either of the groups I play with, but I know them all well enough that's not a concern. In a public game, I'd be more cautious about it, I expect, but I don't think I'd ban it outright.
I do expect that the difference between what the original DM intended and what actually happened is likely a factor. We don't know what that was, though. We only know what the OP shared. Based on what was shared, I don't really see where things would have went differently.
Here are what I see as the decision points for the players, such as they are:
- They could have not surrendered when arrested... but that would have likely resulted in a violent confrontation much earlier, and at a social event rather than a jail.
- They could have not failed to escape the cell. Of course, if they managed to get out of the cell, they'd still have to quietly escape from the jail... and we know how that went.
- They could have turned down the mysterious stranger's offer. This would have left them in the jail cell, waiting for the judge's mercy. We don't know what would have happened here.
- After accepting the mysterious stranger's offer, they could have escaped quietly. It's a bit unclear if they tried and failed to do so, or if they just went into murder mode right away.