I think there have only been two arrests at my schools that I know of, across two different schools.
The first was a case of rape. Apparently a boy forced his girlfriend to give him a lewinsky. They were both minors though, so I'm not really sure if it went to court (I think it did) or what his sentence was, but he didn't come back to the school for 2 years, and when he did he was on a tight leash and basically couldn't leave a very small section of the school.
The second was a fight, where one person knocked the other down and then kicked, and apparently jumped on, his head.
He was arrested for Grievous bodily harm, and I believe sentenced.
Both people were unsavoury characters anyway, and exactly the sort you knew would end up in prison sooner or later.