Why the night?

"Why is it more dangerous at night than in the day?" My friend asked me this question the other day...and we couldn't reach a satisfactory answer.

May it's because ...
1. It is darker, so less visibility, so when bad people do bad things, they are less likely to be seen
2. it's traditionally been that way
3. ghosts and bad spirits come out at night making people do bad things (:P)

Although the most plausible is probably because most respectable jobs are in the morning (because there used to be no lights, so people couldnt' work at night), so people who were awake and moving around at night didn't have a respectable day job. So gradually these people gave the night a bad name?

Maybe one way to make crime rates at night go down is to put more respectable jobs at night. Especially now, when lots of business has to be done with people half way around the globe, working at night doesn't seem to be such a bizzare idea.