Who killed Nice Guy Eddie!?!?!

I watched "Reservoir Dogs" on DVD last night after the rest of the clan went to bed.
Quentin Tarantino's debut feature ends famously, as Joe shoots Mr. Orange, Mr. White shoots Joe and Nice Guy Eddie shoots Mr. White.
That leaves just one unsolved riddle:
Who killed Nice Guy Eddie?
That question has vexed movie lovers since the film's 1991 debut.
I have watched "Reservoir Dogs" probably seven times now and the final scene has always left me scratching my head: Four dead guys but only three shooters. Something's not right!
As related in a special-edition DVD documentary and retold in "The Rough Guide to Gangster Movies," Harvey Keitel (Mr. White) was meant to turn and fire upon Chris Penn (Nice Guy Eddie) after being shot himself.
Filmmakers routinely use a special-effects device called a squib during shootouts. With a squib, a 9V battery triggers a small explosive charge that causes a fake-blood-filled bag to burst. It produces the gunshot and splattered blood effects so beloved by such directors as Sam Peckinpah.
During the famous stand-off scene in "Reservoir Dogs," Penn's squib went off too soon and he fell backwards, covered in fake blood.
Tarantino liked the take and decided to keep it, reportedly telling the cast and crew that he enjoyed the sense of mystery about who killed Nice Guy Eddie.