A federal judge ordered the release of shocking dashcam footage this week showing a Missouri police officer using excessive force in the arrest of a 17-year-old driver, who was tasered for so long he suffered brain damage and almost died.

The officer, Timothy Runnels, was sentenced last week to four years behind bars for the 2014 tasering arrest that put teenager Bryce Masters in a coma.

During the September 14 traffic stop in Independence, Runnels repeatedly used a stun gun on Masters and then dropped the handcuffed teen head-first onto the pavement.

Masters went into cardiac arrest that resulted in oxygen deprivation and brain damage, the Kansas City Star reported.

Excessive force: Dashcam footage recent released by a judge shows officer Timothy Runnels tasering the boy in the car during the traffic stop in September 2014

Shocking: The footage shows the teen stumbling out of the car as the officer continues to taser him

Collapse: The boy is seen falling to the ground shaking after being excessively tasered

Head-first: The cop then handcuffs the boy and drags him over to the pavement and drops him

This is the moment the boy is dropped head-first onto the pavement by the officer, who will now go to prison

Police say Masters was pulled over because of a warrant attached to the license plate of the vehicle and was combative when ordered to get out.

Runnels said he could smell marijuana in the car. In the newly-released dashcam footage, Masters refuses to get out of the car and repeatedly asks whether he is being arrested.

After trying to drag the boy out of the vehicle, Runnels can be heard saying 'f--- it' as he gets out his taser and shoots Masters with it.

The boy then swings his legs out of the car and stands up, while still being stunned.

The footage shows Masters dropping to the ground, and Runnels continues to taser him.

Court filings say Runnels allowed the taser current to run for about 20 seconds, which is four-times longer than officers are trained to have their tasers deployed.

Runnels then handcuffed the teen, lifted his body and dragged him to the curb, before dropping him on the pavement.

Comatose: Masters' heart stopped after he was shocked with the stun gun during the traffic stop in Independence. He was placed in a coma and suffered brain damage

Bryce Masters with his mother. The family issued a statement saying they are pleased the officer has been punished, but wish the incident never occurred in the first place

Off to prison: Independence police officer Timothy Runnels has been sentenced to four years prison for his use of excessive force in the arrest of the teenager

After a few minutes Runnels called for an ambulance but did not check on Masters, KCTV reported.

When the ambulance arrived, Masters was in cardiac arrest. He was taken to a hospital and placed in a medically induced coma.

At the trial Masters testified that the damage done to his brain during the incident could affect him for the rest of his life.

The Masters family gave this statement following the release of Runnels' sentence.

"While we are pleased that Mr. Runnels was held accountable for his actions, no one really wins in this scenario,' the statement said in-part.

'Two law enforcement families were devastated by these events and we all simply wish that day had never happened."

In footage taken by a witness, Runnels (pictured) is seen raising his foot as Master lies on the ground

At the time of the arrest, police said Masters had suffered a 'medical emergency' and needed resuscitation.

But eyewitnesses gave a different account to Fox4KC.

Michelle Baker filmed the incident on her mobile phone when she heard screams outside and says she saw the Runnels Taser the teen when he was inside his car.

In a cell phone video taken by Baker you can see the officer dragging the teen's body to the sidewalk, then standing with his foot on the teen's back.

You could tell the kid was going into convulsions.

'He turned him over and his head was dangling like this and he had blood coming out,' said Baker.