Driver was being held hostage by robbers. Regardless whose rifling marks are on the bullet, the robbers are the ones who are at fault here. The law has set this precedent many moons ago, and it’s still how the business is done. They’ll go down for murder, unless some weasel of an attorney goes for plea bargaining.
Part two of this, is the investigation.
With that many shots being fired, this could take weeks to put each bullet back “into” each gun. And the “offending” bullet may be too damaged to fully identify which gun.
This isn’t a hour long process like TV, while they can actually match bullet material to barrel residue, the problem with this is that all the department guns and ammunition will have the same residue in each gun.
I.e.: AR15 A was fired with X bullets and contains B residue.
AR15 D and G were also fired with X bullets and have B residue as the ammunition came from the same manufacture batch.
At this point, if you cannot identify using rifling marks, or bullet trajectory which gun was used, you will not be able to identify which person fired the shot.