Authorities are still trying to figure out the circumstances surrounding a bizarre police-involved shooting in East Tennessee where an officer got into the bed of a pickup truck and shot and killed the fleeing driver.

Questions remain about how Lenoir City Police Officer Tyrel Lorenz wound up in the bed of the Dodge Dakota and what prompted him to reportedly shoot inside a moving vehicle. The pickup at one point was driving into oncoming traffic and then crashed into a utility pole just after 1 a.m. Sunday in Lenoir City, a town about 30 miles southwest of Knoxville. But investigators have to determine whether the driver, 30-year-old Joshua Grubb, was fleeing into oncoming traffic or if Grubb lost control of the vehicle after he was shot and the pickup careened into opposing lanes before crashing. Police initially said Grubb was from Lebanon but they have determined that he lives in Clinton.

Loudon County District Attorney General Russell Johnson has asked the Tennessee Bureau of Investigation to probe what happened.

Most progressive police agencies across the country bar officers from both getting into the back of a fleeing car or firing into moving vehicles because of the danger it creates to the public, one law enforcement expert said.

"Why would you jump into a moving vehicle? That's what we call officer-created danger," Geoffrey Alpert, a professor of criminology at the University of South Carolina, said. For that reason, Alpert said, it's important to find out what exactly happened in this case.

Lenoir City Police chief Don White said the department had no policy on officers shooting at moving vehicles.

Lorenz, 29, had been on the force since July 2015, a statement issued by Johnson and White said.

The incident began with a 911 call that reported intoxicated people in a pickup truck, Chief White said.

Lorenz stopped at the Bimbo's gas station and convenience store on Highway 321 and found Brandon Lawrence Taylor pumping gas into the truck, Grubb sitting inside the driver's seat and another passenger, Toni Ann Sutton, inside the store.

Taylor, a 31-year-old also from Clinton, showed signs of being intoxicated and Lorenz placed him under arrest, White said. He was later charged with public intoxication.

"He was trying to approach Mr. Grubb on the driver's side of the vehicle, and that's when Mr. Grubb decided to flee in the vehicle," White said.

The chief said it's not clear how the officer wound up in the bed of the pickup and there were really tight conditions between the gas pump and a curb.

One question that is being looked at is how fast Grubb was driving, TBI spokesman Susan Niland said in an email.

Lorenz repeatedly yelled for the driver to stop. The officer fired repeatedly inside the cab of the pickup after Grubbs refused to stop the vehicle, authorities said.

The truck, the statement said, went down the wrong side of Highway 321 before hitting a utility pole.

Officials said they still have to complete the autopsy, conduct forensic analysis, complete interviews and go over video camera footage to determine what happened. Prosecutors plan to present the evidence to the Loudon County grand jury at the next meeting in April.

Lorenz is on paid administrative leave.