In my jurisdiction, if one causes a death while committing any very serious crime (carrying a penalty of 20+ years' imprisonment), then it is said to be a "constructive murder" (i.e. the law constructs the charge of murder; used to be called "felony murder"). The classic example is if I rob a bank and the security guard fires at me, misses, but hits & kills a bystander, I will be charged with their murder.

The key here is "causes". If both were tried for this murder, then each could say in their defence there is reasonable doubt as to whether they rather than any of the other shooters caused the death. If guns were recovered then I imagine there are a lot of ballistics matching going on right now.

One way around this might be if the prosecution can determine who fired the first shot, even if that wasn't the fatal shot. They could argue this was the act that caused the other shots including the fatal one, and was therefore the cause of the death, therefore establishing murder.

I'm assuming there is a felony/constructive murder charge where you are, and that the principal offense (attempted murder of the intended target? assault with a deadly with intent to kill?) is sufficient to trigger it. If I'm wrong on either count, then as others have said this would probably have to be charged as a manslaughter, but everything I've said re. causation still holds.