HUMBLE, Texas -- A man who witnessed a gas station robbery was killed after chasing the crook, KPRC Local 2 reported Wednesday.

Police said it happened Tuesday night at about 7:15 p.m. at a Shell gas station located at 1003 FM 1960 East and North Avenue H.

Investigators said Steven Jackson, 47, was putting gas in his vehicle when a cashier ran out of the Shell screaming that she had been robbed. Police said Jackson got into his car and followed the robber for at least half a mile while on the phone with a 911 operator.

"He knew that something wrong had taken place and it's my assumption that, in the 911 call, he was trying to give a description of the vehicle," said Holly Jackson, the victim's wife.

Officers said the robber got out of his vehicle in the 21000 block of Highway 59 at Jensen Road and fired two shots at Jackson, who died at the scene.

The gunman is still on the run. Police said they do not have much of a description of him.

Jackson was a volunteer firefighter in Porter and known for helping others.

"He was always interested in helping other people. He would go out of his way to help other people," Holly Jackson said. "I hope they capture whoever did this and I hope they're punished for it."

"No one is going to stop remembering my dad. No one is going to stop fighting for him, fighting for what he believed in," said Blake Jackson, the victim's son.

While police applaud the victim's desire to help, they said that if you get into a similar situation, give authorities a description and tell them which direction the perpetrator was headed. Authorities said law enforcement should handle it from there.