The last 3 rounds were fired from BG#3 - the getaway driver. He lays his pistol almost on top of the vehicle above the driver's side door and fires 3 shots. The flash from one of the shots is seen in the video.
Also - while the getaway driver was shooting, BG#2 was jumping around and pointing his handgun in the direction of the store.
I don't think BG#2 had a functioning firearm. As soon as the gaurd pulled his weapon, BG#2 ran from the store. Both BG#1 and BG#2 pointed their weapons at the SG and back into the store as they exited (I won't say retreated).
It brings up a point for me. Given that as a group - this group of 3 criminals continued the attack after BG#1 was shot, I'm not sure if you even get into considering any 1 particular guy as being in the process of retreating.
SG was under attack from a group. Given that he was either under fire or had one BG or another pointing their weapons at him, they never really retreated until the car started moving, and SG had long since stopped firing.