Cop stuns teen for 21 seconds sending him into cardiac arrest, causing brain damage (VIDEO)

KANSAS CITY, Mo. -- A federal judge has released a police video showing an Independence, Missouri, officer using force and a stun gun on a teenager who went into cardiac arrest.

Former Independence Officer Timothy Runnels was sentenced last week to four years in prison after pleading guilty to violating the civil rights of 17-year-old Bryce Masters during a 2014 traffic stop.

The Kansas City Star reports the video was played during Runnels' sentencing hearing and was released by the judge Monday.

The video shows Runnels using the stun gun on Masters. After Masters goes limp, Runnels can be seen handcuffing the teen and dragging him to the curb, where he drops him face down on the pavement.

Masters went into cardiac arrest. He testified that he's become forgetful and has difficulty focusing.