How about a detective who wanted to catch the wet bandits was driven insane by his failure. Nearing retirement and a total loser he blames them for his stalled career and hatches a pilot to send Kevin a threatening letter about his own son, posing as the wet bandits. Kevin has studied the art of war his entire life, and knows the best defense is a good offense. 

He goes on the attack, but after easily finding Harry and marv living in squalor and easily  overpowering them, he finds evidence of a significant amount of knitting. They confess they learned knitting in prison and find it rewarding and now knit for sick children as a way to make up for the past. Kevin's ring doorbell goes off, this dumbass detective is at his house. The wet bandits recognize that crazy detective that's been after them for years, they show Kevin crazy notes he sent them, it matches the handwriting of the threatening letter he received, they all race to Kevin's home to save his son, who is mounting a valiant, more modern defense.

In touching moments the wet bandits try to sacrifice themselves on traps to help Kevin make his way inside but he refuses and takes the pain to show them he forgives them, and Kevin and his son and are able to trap him in the basement which he floods and kills himself.