There had been that Weapons Law, for a start. Weapons were involved in so many crimes that, Swing reasoned, reducing the number of weapons had to reduce the crime rate.

Vimes wondered if he'd sat up in bed in the middle of the night and hugged himself when he'd dreamed that one up. Confiscate all weapons, and crime would go down. It made sense. It would have worked, too, if only there had been enough coppers - say, three per citizen.

Amazingly, quite a few weapons were handed in. The flaw, though, was one that had somehow managed to escape Swing, and it was this: criminals don't obey the law. It's more or less a requirement for the job. They had no particular interest in making the streets safer for anyone except themselves. And they couldn't believe what was happening. It was like Hogswatch every day.

Night Watch, Terry Pratchett