FORT LAUDERDALE, Fla. – A stranded motorist walked toward a Florida Highway Patrol trooper and suddenly shot him, a fatal attack that led to an Interstate 95 shootout with a police officer that also left the gunman dead, an investigation released Friday concluded.

Trooper Joseph Bullock had been helping Franklin Reed III for an hour Feb. 5 and had returned to his patrol car to do paperwork when Reed, after a dispute with a tow truck driver overpayment, walked over and shot him in the head, Martin County Sheriff William Snyder told a press conference.

Snyder called Bullock's slaying “an unprovoked, premeditated murder.”

Snyder said Bullock's interactions with Reed, 30, had been routine. About 9:15 a.m., Bullock spotted Reed's SUV parked at a 90-degree angle on the northbound side of a tree-lined swale that separates the lanes of I-95 near Palm City, about 40 miles (64 kilometers) north of Palm Beach.

A soundless dashcam video taken from Bullock's patrol car shows the 42-year-old trooper stop near Reed, walk up and have a normal conversation with him that lasts minutes. Reed apparently told Bullock he thought he could get the SUV running, so Bullock drove away.

About an hour later, a motorist told 911 that Reed's SUV appeared to have been in a crash. Bullock returned and found the SUV further down in the swale. He called for a tow truck to assist Reed, who had no criminal record and a concealed weapons permit.

Bullock remained with Reed for the next hour without apparent incident before the tow truck arrived. As the tow truck driver hooked up Reed's SUV, Bullock went back to his patrol car and sat in the driver's seat. The tow truck driver told detectives that Reed became upset because he didn't have enough money, but he didn't think there was any danger as he followed as Reed walked toward Bullock.

Reed pulled a gun and shot Bullock and then turned his gun on the tow truck driver, but it jammed, Snyder said. The tow truck driver ran through the trees to the other side of the swale and waved for help along the busy highway, gaining the attention of passing motorists including Riviera Beach Police Detective Jemel Headings, who was driving to work.

Headings spotted Bullock lying on the ground next to his patrol car, so he made a U-turn through the swale. As he called 911 to get assistance for Bullock, he spotted Reed, who pointed his gun at him, Snyder said. On the 911 call, Headings can be heard yelling at Reed to drop his gun before an exchange of gunfire erupts. Snyder said Headings shot Reed in the chest, a wound that would have been fatal if Reed hadn't then shot himself in the head, dying instantly.

Snyder said Headings did a “phenomenal job” as he came upon a confusing situation where he thought he was assisting an injured trooper only to find himself confronting a gunman “who had nothing left to live for.” He said if Headings hadn't engaged Reed, there likely would have been a larger shootout as a swarm of law enforcement soon arrived.

“There would have been rounds flying all over that interstate,” Snyder said. “The actions of that off-duty detective were life saving.”

Snyder said it was later learned that Reed had stolen a gold medallion the previous day from a store, but he didn’t think that played any role in the shooting. He said toxicology tests to determine whether Reed had used drugs are still pending.