unnamed man was found dead from an apparent self-inflicted wound around 5 p.m. on sunday .
incident happened near the buffet at the m resort spa and casino in henderson , nevada .
witness describe hearing a large boom and then seeing a man lying on the ground with a pool of blood surrounding his salt-and-pepper hair .
a car fire was reported at the same time in the parking garage , and police are investigating if the two incidents are related .