If it were CSI... since the guy in the driveway knows how to use guns, he stole the neighbors gun, drugged him, put him in the car, shot him, planted the gun, wrote a fake suicide note, and went to work on his car so he would have an alibi.
The cops were taking precautions because they didn't know if the guy in the driveway would start shooting if they accused him of murder.
I'm just guessing here, but maybe the police worry about you selectively editing the video tape, or adding in something that didn't happen. But the securing the area thing doesn't sound right.