Hostages and Getaway Cars

I know this happens a lot in movies, but I’ve also seen it happen IRL (the recent German hostage-taker, for example). Someone will go nuts and take hostages in some local building. They’ll sit around in the building and make various rants to the media, negotiators, etc. and eventually demand something like a getaway car, helicoptor, etc. What I’m wondering is how often does the person manage to get away in the getaway vehicle? I mean, sure, they successfully get some food for themselves and the hostages while the situation is on, but it seems to me that it would be virtually impossible to actually get away in a police supplied getaway vehicle.

I’m not interested in things like international hijackings, where the person goes off to another country, just the ones that are pretty much local.

No.
http://www.cnn.com/WORLD/9612/31/mexico.robbery/

Yes.
http://ca.news.yahoo.com/020403/5/lga2.html