A little while later, the guard confronted the father and son because they were relieving themselves in the parking lot.
An altercation followed, in which the guard reportedly pepper sprayed the son. The father got upset and began threatening the guard, saying he was going to kill him. He left and came back with a gun.
"The security guard ordered him to drop the gun and he did not, at which time the security guard discharged his own weapon," said Sgt J.C. Padilla with the Houston Police Department.
The guard shot the father in the head one time, killing him. Right now, the guard isn't facing any charges. Police believe he fired in self-defense.
The son, who witnessed everything, has been questioned by police.
Police have wrapped up their investigation at the scene and say the killing was pretty much a senseless act.