HOUSTON -

Houston police began an internal investigation Wednesday morning after a security guard shot and killed a homeless man.

Investigators said the guard was patrolling a strip center in the 4400 block of I-45 near the intersection of East Crosstimbers Street.

He noticed a man, who was believed to be homeless, curled up next to one of the stores. The guard called Houston police and attempted to wake up the sleeping man.

When an officer arrived, he shook the man awake and informed the man that he needed to leave the property.

According to investigators, the suspect jumped up and attacked the officer, punching him in the face.  The officer then retreated behind his squad car, where he requested backup. At that time, the man turned toward the security guard and began attacking him as well.

The security guard fired one shot into the man's abdomen.

The shooting victim was rushed to Ben Taub Hospital, where he later died in surgery.

Even though the security guard isn't affiliated with the Houston Police Department, officials decided to conduct an internal investigation because a Houston officer was at the scene when the shooting occurred.