Well, that's the official story given by the police. According to the protest medics who treated the shooting victim on the scene, the cops took so much time getting ready to respond - and this was independently verified by a local journalist, using hospital intake records and police scanner timestamps - that the medics gave up on the ambulance and drove the man to the ER themselves. When the police finally showed up, they were in fact told to leave, but it was not out of some political objection to emergency services: they were simply far too late to be of any use to someone who was already in the hospital at that point.

(I live just up the street from the police station at the center of the whole thing, so I paid close attention to all this stuff while it was happening.)