Questions (possible plotholes) about the serial killer's tactics

Why did he suddenly decide to kidnap someone for money? He was only interested in killing people up to that point. It can't have been to provoke the cop, there's no way the serial killer knew the cop would be assigned to the case.

And why did he kill the girl in the bus? Was it to mess with the gangster? Or was it a coincidence that he happened to be on the same bus that was boarded by the girl after she took the umbrella from the gangster?

Lastly, is he scared of dying? He doesn't seem to be when the gangster catches him, or when he is arrested. He even confesses in custody. But then he suddenly wants to avoid the death row. And he is visibly nervous when the gangster shows up in the same prison. Pretty inconsistent characterization there.