Problem with morgue and hearse?

So I have started building a new prison, but I have a problem with dead bodies. They get transferred to the morgue fine, but then a hearse comes every 15 minutes or so and just sits outside 'processing'. But then after a while it just drives off and the bodies remain in the morgue.

I've tried rebuilding the morgue, building a new morgue (see by the prison entrance) etc. and nothing seems to work. I've got enough free guards so there isn't a problem with transporting the bodies neither.

Any ideas? See below for a pic. http://imgur.com/a/EEQvj