(CNN) A gunman is on the run after killing two men on a Houston freeway as horrified motorists watched during the Thursday evening rush hour, authorities said.

Police initially got a call of an accident at 5:55 p.m., but when they arrived seven minutes later, they found a shooting scene.

The fatal incident started as a crash involving two cars headed eastbound on Interstate 10, Houston Police Assistant Chief Bobby Dobbins said Thursday evening at a news conference.

"One of the vehicles struck the other vehicle and spun it out ... similar to a pit maneuver," he said. A pit maneuver is a police tactic used to spin out a car from behind during a chase.

Gunman fired as the car rolled downhill

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