

Nick is playing judge, jury and executioner in unison. Nick effectively executes Clyde for what he's done, without a trial. So when Nick gives Clyde a last chance to give up before actually deliberately blowing him up, he has crossed this line. There simply seemed to be no way to stop this guy with legal measures. He forced the police, the attorneys, and the entire city's government into a corner from which they couldn't get out.
#Cast of law abiding citizen movie
Throughout the movie he tried to show everyone how broken the system is, he made deals for trivial commodities and baited a judge into giving him low bail, only to then insult her for her lack of justice, and ultimately comitted all his crimes being locked up in prison.

He wanted to drive the law enforcement system to its extremes, so that they finally realize what is "necessary" (from his point of view) to stop somebody and enforce true "justice", and not hide behind their supposedly broken system anymore, which was what he primarily blamed for the lack of justice the murderers of his family got. The primary motivation why Clyde did this was not only revenge, but also to prove his point. However, there is yet another aspect to this. 22, 2021 Read today's 'The Armed Citizen' entry for real stories of law-abiding citizens, past and present, who used their firearms to save lives. Engineer, Clyde Shelton, played by Geral Butler, is forced to see his daughter and his wife killed in front of his own eyes.

And I also agree that it surely isn't really guilt over what he did. Burhan already makes a great point in that Clyde was merely exhausted from his anger and had nothing to live for anymore, so he was partly relieved to finally die and get back to his family, something he himself couldn't and wouldn't do.
