Why stab him after a head shot!?!
Fucking idiots…

Maybe they've heard about "Gemini method"?
https://en.wikipedia.org/wiki/Roy_DeMeo The process of the Gemini Method, as revealed by multiple crew members and associates who became government witnesses in the early 1980s, was to lure the victim through the side door of the lounge and into the apartment in the back portion of the building. At this point, a crew member (almost always DeMeo according to crew-member-turned-government-witness Frederick DiNome) would approach with a silenced pistol in one hand and a towel in the other, shooting the victim in the head then wrapping the towel around the victim's head wound like a turban to stanch the blood flow. Immediately after, another member of the crew (originally Chris Rosenberg, up until his 1979 murder, according to government witness testimony) would stab the victim in the heart to prevent more blood from pumping out of the gunshot wound. By then, the victim would be dead, at which point the body would be stripped of clothing and dragged into the bathroom, where the remaining blood drained out or congealed within the body. This was to eliminate the messiness of the next step, when crew members would place the body onto plastic sheets laid out in the main room and proceed to dismember it, cutting off the arms, legs and head.[25]