Turner, 47, told dispatchers he was being followed after some kind of confrontation before getting onto the highway around 3 p.m.
He told police someone in the other car -- it was unclear if the it was the driver, or if there were other people in the car -- brandished a semi-automatic weapon at him.
Then, they shot him.The person in a gray, newer-model Ford Taurus with tinted windows pulled aside Turner's car, firing several shots, Hillsborough County Sheriff's deputies said. Turner was able to pull over to the shoulder, where he died.
"The caller stated that he had done nothing to cause someone to follow him," said sheriff's spokeswoman Debbie Carter.
"We're going to have to reconstruct [exactly what happened] from the 911 tapes," said Sheriff David Gee. "We know that we have the shooting apparently on the tape."
Police asked the public to report anything they might have seen that could help track down the as-yet unknown suspect.