I took something out of a policecar, and and another Item respawned instantly while I was infront of the car. I tried it out and took all the stuff from the car, layed it a few meters besdide the car on the floor and when I headed back to the car, new loot was spawned. I did this for maybe 30-40 minutes and generated in this time five MP5, seven CR75, a few stabvests, flashbang grenades and other random policestuff. It felt like that the spawncuircles slowed down a bit after maybe 20 minutes, but it spawned loot again and again.
I tried it only a one policecar but here it was 100% reproducable. {F32857}