OKLAHOMA CITY - A state politician was stabbed to death Sunday evening at a northwest Oklahoma City fast food restaurant, sources tell News 9.

Oklahoma Commissioner of Labor Mark Costello died Sunday evening after being stabbed at Braum's, 11224 N May Ave., Oklahoma City police Capt. Paco Balderrama said.

About 6:35 p.m. Sunday, police were called to the Braum's in reference to a man stabbing another man inside and outside the restaurant.

Earlier in the day, two family members had a fight with one another and agreed to meet at Braum's. When the two arrived, one stabbed the other multiple times in the head and neck with a steak knife, police said.

The stabbing started inside the restaurant and continued into the parking lot, where other customers tried to stop the assault, police said.

Patrick Spencer was driving by and saw the two men walking around the restaurant. Costello was bleeding and his son followed him. Spencer witnessed Costello being stabbed in the head.

“It was shocking and dramatic and like I said, it was very cold and you could feel the sense of cold,” Spencer said. “Several people were able to step in and get the knife away from him and tackle him to the ground and they tied him up with belts.”

Costello was taken to OU Medical Center, where he died.

Police arrested Costello's son, Christian Costello, 26, in connection with the stabbing death, Balderrama said.

Stay with News 9 and News9.com for more information as it becomes available.