A former Missouri police officer has pleaded guilty to violating the constitutional rights of a minor by deliberately dropping the restrained teenager face-first onto the ground.

Federal prosecutors in Kansas City on Friday announced that former Independence officer Timothy Runnels admitted his role in a Sept. 14, 2014, confrontation with 17-year-old Bryce Masters.

Prosecutors say Runnels used a stun gun on Masters during a traffic stop even though the youth was not a threat. Masters then dropped Masters face-first while he was restrained. Masters went into cardiac arrest and was placed in a medically induced coma and treated for lack of oxygen to the brain.

Runnels was indicted in March on four federal charges accusing him of using excessive force and hindering the police department's investigation of the incident.