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AURORA, Colo. (KDVR) — William Farnsworth has had to pull out his gun many times as a bounty hunter, but the 23-year-old said he never thought the first time he would shoot someone would be on a moving RTD bus in Aurora.

“I tried my best to defend myself before I used a weapon, and, in the end, I had to shoot him,” Farnsworth said in an exclusive interview with the Problem Solvers.

“I was losing consciousness, the man was on top of me beating me senseless and he said, ‘I’m going to kill you.’ And I told myself, ‘If you lose consciousness, he’s going to follow through with that threat,'” Farnsworth said.

Farnsworth was riding the bus July 9 with his wife and 18-month-old daughter when he said he and his wife asked a young couple on the bus to stop vaping because it’s not allowed.

“He ignored us until the third time we asked him. He stood up and he said, “F— you, f— your wife and f— your baby.’ And he started swinging at my wife and baby first, and I had to throw myself in-between them,” Farnsworth said.

Farnsworth then took out his gun and shot the unidentified teenager once in the chest.

“He said, ‘You shot me’ and walked off the bus and lied in the grass. Made no attempt to put pressure on the wound,” Farnsworth said.

Aurora police said the teen has since been released from the hospital and now faces a misdemeanor count of assault, but because he’s a juvenile, his name is not being released.

“I acted in self-defense, and most of the officers on the scene told me they would’ve done the same thing,” said Farnsworth.

The Problem Solvers made a public records request for the bus surveillance video, but an RTD spokesperson told FOX31 the footage would not be released because it’s part of a pending criminal case.

However, law enforcement sources told the Problem Solvers the surveillance video backs up Farnsworth, who insisted he had no choice but to use deadly force when he was attacked.

When asked if he would ever say anything to someone vaping on a city bus in the future he replied, “We might say something to the bus driver, but we’re going to try and avoid people in general.”

Even though Farnsworth faces no charges, he’s been told he can’t have his Glock handgun back until the case against the teenager is adjudicated because prosecutors need the gun as evidence.