"...a 25 y.o. man was shot multiple times in the head..."
The Chicago Outfit used several .22 LR, usually Remington Gold Tip hollowpoints. (The gilt paint flakes off and spoils the forensic analysis.)
The ballistics allows for only one bone penetration, and just bounces around inside the cranial vault. The brain itself is only the consistency of Camembert cheese, so you can get two or three skips. The tears in the skin are small and don't bleed much.
The Outfit only used a shotgun when they wanted to send a message. Mad Sam DeStefano was all but shredded with a pump gun. Same with Roger Touhy, and Manny Sklar...
Of coarse, that was back when they had pros, and they only whacked their own.