i'm no lawyer (nor do i ever want to be) but with criminal defense lawyers pretty much at the top of the heap when it comes to making money, it seems like there are a lot of well paid people out there to come up with a defense for pretty much every situation (including those you mention). if there's physical evidence, then someone planted it. if there's video and eyewitness testimony, then the person was insane when he/she did it. etc.

in these cases where the majority of these attacks happen at night (yeah i know this thread was at 2:30pm on a saturday), it's hard to get any kind of really clear evidence. it's night so you can't really see them very well, nobody has video footage but even so, it's still dark so they can argue that it's not me but another guy with the same race, etc. i'm in favor of the death penalty but i don't think as many cases are 100% cut and dry as we think they are.

i think maybe bikes equipped with lojack might help bring down some of these guys. of course they'll just claim that they bought the bike or found the bike, etc.