A federal judge on Monday unsealed disturbing dashcam footage of a suburban Kansas City, Missouri, police officer tasering a 17-year-old motorist who became brain damaged after what was billed as a routine traffic stop. That stop subsequently turned into an event of excessive force—resulting in a four-year prison sentence for Officer Timothy Runnels of the Independence Police Department.

The video shows Runnels tase and yank Bryce Masters out of the car and down on the street as Masters howls. The boy was filming the officer with his mobile phone, which the officer flings to the street. "Am I under arrest? Am I under arrest?" the teen is overheard saying before he is stunned and grabbed from the vehicle.

The officer drags the boy on the street like a sack of potatoes then drops him face first to the ground. During the brief 2014 incident, the boy, who was going to play Xbox with a friend, went into cardiac arrest and now suffers from brain damage. The traffic stop was based on a warrant from Kansas City, which turned out to be a mistake connected to the license plate on the vehicle the boy was driving. The officer claimed he also smelled marijuana and that the teen was being uncooperative.

The boy nearly died and was placed in a brief medically induced coma. The stun gun discharged and hit the boy near his heart for 20 seconds. He can be overheard weeping as the officer drags him following the Taser hit.

Local authorities did not prosecute Runnels. So the Justice Department, having dashcam and eyewitness evidence in hand, took the case to a federal grand jury which indicted the officer last year on two counts of excessive force and one count of falsifying the account. "Specifically, the defendant authorized and submitted a false and misleading official police report, which falsely described and omitted details concerning the force that he used against B.M. on September 14, 2014, and the circumstances that led to B.M.'s bodily injuries on that day, with intent to obstruct any investigation into the deprivations of constitutional rights described in Counts One and Two of this Indictment," according to the indictment (PDF). The officer agreed to plead guilty (PDF) to a single excessive force count in September and was sentenced June 1.

"This former police officer was trained and entrusted to enforce the law impartially," said US Attorney Tammy Dickinson. "His use of excessive force violated both the public’s trust and his oath to uphold the law. Police officers are not above the law and will be held accountable when they violate the civil rights of the citizens they are sworn to protect and serve."

Police originally said, "Officer Runnels instructed the driver to move to the curb. Officer Runnels stated that the driver did not comply with his command, at which time, he grabbed the driver from behind and carried him to the side of the roadway."

US District Judge Dean Whipple ordered (PDF) the release of the dashcam footage Monday after the officer's attorney decided not to challenge its release.

At a court hearing last month, the boy told the judge that "People tell me I'm different. I feel different." He said he is forgetful, withdrawn, and weak. Masters said he has nightmares and no longer plans to attend college.

"I get in the car to go somewhere and then I’ll forget where I was going," he said. "I’ve missed job interviews because I forgot them."

During that same May 26 sentencing hearing, the defendant said he was "deeply remorseful" and "at no point did I intend to hurt him, but I did."

The officer remains free on bond and must surrender to federal prison in August.

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