Okay (thanks for the closeup pic) I count no fewer than 12 separate holes aside from the one big ragged one. They seem to be pretty big for an entrance hole. Perhaps a .45. But if it was a 45 then it was a high cap 45 and that makes it....an interesting array of possibilities.
Is there any definitive statements as to whether this was a handgun or maybe a small machine pistol like a Skorpion? Maybe a micro Uzi? Neither of which is chambered in the 45. I was thinking it reminded me of a shotgun slug (the big hole) followed by a bucksot pattern.