(CNN) A veteran Florida trooper was fatally shot on Interstate 95 after pulling over to assist a disabled vehicle, police said.

A passing off-duty police officer from another jurisdiction witnessed the shooting and killed the suspect, said Col. Gene Spalding, director of the Florida Highway Patrol. The suspect was later identified as Franklin Reed III.

The highway was shut down for several hours Wednesday as investigators processed the scene, which unfolded in the shoulder of the northbound lane, about 6 miles west of Palm City.

Trooper Joseph Bullock, who spent 19 years with the highway patrol, saw what he thought was someone having car trouble about 10:15 a.m. He pulled over to help, and "the suspect who was with the disabled vehicle shot him, resulting in fatal injuries," Spalding told reporters.

Several law enforcement agencies responded to the highway slaying.

"A Riviera Beach police officer who was passing by engaged the suspect, fatally shooting him," he said.

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