An undercover West Valley City police officer was justified in the fatal shooting of a man who hit his partner with his car following an alleged drug buy, the Salt Lake County District Attorney said Friday.

Three undercover officers were in a Burger King parking lot on Jan. 27 when they saw 39-year-old Travis Paul Johnson drive up and buy heroin from someone in another car, police said.

After watching the sale, the officers walked up to Johnson's Pontiac Grand Am and identified themselves, police said.

Johnson backed up the car, and when an officer put his hands on the car hood to stop him, he accelerated rapidly, running over the officer's foot and knocking him down, police and a nearby business owner told the The Salt Lake Tribune .

Fearing Johnson would run over the man, his partner and fired into the car, striking Johnson. He was taken to Intermountain Medical Center, where he died of his injuries.

Johnson's willingness to hit police with his car justified the officer's belief that deadly force was necessary, said Salt Lake County District Attorney Lohra Miller in a statement.