Unsub fires 4 rounds at mail carrier then minutes later fires 14-15 rounds at the team thru a door. After a few more seconds pass he fires another 4 rounds thru door for a total 22-23 rounds. The unsub had a H&K USP45 that holds 12+1 rounds and would have needed to reload his weapon but never did.
Unsub fires 4 bullets at the mail carrier killing him. The gun is in battery (slide forward) the camera angles change and you can clearly see the gun is now out of battery with a piece of brass stuck in the chamber (stove piped). The camera changes angles again and the gun is back in battery without the unsub clearing the gun.