Shoot him in the extremities and let him writhe in pain until he dies. A bullet in the head is too good for him.
take him out in the woods and bury him in concrete feet first just few inches up past his knees so he cant sit down and ties his arms back.
Let the crows take care of the rest.
A round in each knee, and each ankle, and each elbow, and each wrist. It won’t kill him, but watching him “get around” will be entertaining.