Seems appropriate to me. Person was holding a gun while doing a robbery which greatly amplifies the danger inherent in the crime they were doing.

On the flip side, I knew someone who interrupted a car burglary and was murdered by the burglar. Imagine what might happen if someone came upon the guy you know of who was doing a robbery while holding a stolen gun?

The person you knew made a lot of choices that led to this, any of which had they not chosen to do would have led to not being an armed robber: don't do a robbery, don't steal a gun, don't do a robbery while holding a gun.