HOUSTON – A Harris County Precinct 5 deputy constable opened fire on a suspect and killed him Thursday afternoon in southwest Houston.

The deputy with the toll road force pulled over a vehicle on Beltway 8 near Bellaire Boulevard. The deputy detected the odor of marijuana. After the driver refused to get out of the car, he started the vehicle and began to drive off.

When the suspect's vehicle pulled away, the deputy was dragged.

"As he is hanging onto the car, the suspect reached for the deputy's gun hand. When he feels the suspect reaching for his hand, he then discharges his duty weapon, striking the suspect," Kese Smith of the Houston Police Department said.

The officer fired one round -- killing the suspect. He has not been identified.

The deputy was not injured.

The Houston Police Department Internal Affairs Division and Harris County District Attorney's Office will investigate.