Attempted murder *spoiler*
Why did Callahan try to kill Hiro and the gang multiple times? His entire grudge was against Krei, his revenge plan against him is partly justified but doesn't seem to involve harming Krei physically until the end. But while the kids are investigating him, he seemed to want to straight up kill the gang. Sure he could have been trying to scare them off, but the way he was going about it, one wrong move by the gang and they would have been killed.
So why was he trying to kill them?
Florida! But that's Americas wang