I tried to look at the video for clues about the first shot and I can't figure it out from that alone
Its about 1.2 seconds between the gun leaving the guy's waistband and the first shot, and another 1.5 seconds to the first of the next round of shots
Its not clear if any body language and reactions are from the gunshot or impact, if Pretti was shot or not. I don't see an obvious wound like after the next few shots.
The officers very clearly respond involuntarily to the first shot. One guy standing up swings his hand, hitting another officer on the head and pushing him down forwards, and he appears to let go, same with another and Pretti gets up on his knees. Possibly in response to the gunshot sound, possibly in response to being shot. There's some artifacting and lens glares at that moment, but they track with movement of the camera rather than being any kind of splatter, and you can see the breath of the people as they exhale in the cold so there's plenty of particulate already in motion visible. The recoil and some very light flare is visible for one frame of the second gunshot, very clearly from the officer's gun behind Pretti, which immediately downs him.
I think the question of whether his gun was fired or not is still the biggy, its the difference between "Jumpy officer shoots him just because the other cop shouted 'gun gun gun'" vs "He opened fire only after hearing gunshots and thinking Pretti was going rambo"