[oh8eleven]

Capt. Huff believed Wallace was either about to or had already harmed the child with the knife. He approached Wallace as he was seated in the chair, and shot him in the head. Wallace was killed instantly.
In before the "why didn't they taze him ~OR~ why didn't they shoot him in the leg?" idiots.

[Greysard]

In before the "why didn't they taze him ~OR~ why didn't they shoot him in the leg?" idiots.

"His leg was not guilty of anything. It was the head that committed the crime."

[societyisdense]

They shot him in the head because he deserved it. He had an innocent two year old child sitting on his lap and getting him right in the head forces his arms to drop considering he is dead on impact. If he was tazed/shot in another area of the body- he is still capable of moving his arms freely, which had a KNIFE in it, thus causing potential harm to the child.