I think you're right. That's a most probable scenario, based on released information.
I though that too, but these lines from the story don't support it.
"Before his capture, Sgt. Walters was shot in the leg and stabbed three times in the abdomen with a bayonet, Maj. Strong said, citing the report. It was not clear whether the bayonet wounds would have killed Sgt. Walters. He was held separately from the other soldiers, but was seen being led into the building and his body was brought out".