A Calgary police officer has been convicted of aggravated assault for his actions during a violent arrest that left a man with a fractured skull and brain injury.

Const. Trevor Lindsay faced a trial last month after he was charged following the May 2015 arrest of Daniel Haworth.

Court of Queen's Bench Justice Michael Lema delivered his decision Friday morning in Calgary.

Lema said Lindsay's use of force was "unnecessary and excessive," adding that no aggressive measures were warranted in the arrest.

Daniel Haworth suffered a fractured skull and brain bleed at the hands of Calgary police officer Const. Trevor Lindsay. (Court exhibit)

On May 25, 2015, Lindsay and his partner arrested Haworth for theft, suspecting him of breaking into his ex-girlfriend's home and stealing coins from her collection.

Haworth was taken to the arrest processing unit (APU). Surveillance video from the neighbouring library shows what came next.

In the parking lot, Lindsay pulls the handcuffed Haworth out of the police car and presses him, face first against the cruiser.

He punches him once, then three more times in quick succession before swinging Haworth to the ground, head first.

Lindsay testified in his own defence, telling the judge that after he punched Haworth, his arrestee had tried to spit blood at him so the officer said he felt an aggressive take-down was warranted.

This graphic security footage shows what appears to be a Calgary police officer punching a man repeatedly before throwing him on the ground. 0:42

Though it was supposed to be a "controlled takedown," Lindsay said he accidentally lost his grip on Haworth, who was handcuffed and was whipped onto the pavement head first.

Paramedics were called and Haworth was taken to hospital. Haworth suffered a fractured skull, brain injury and his brother testified he was never the same after the injuries.

Haworth didn't try to spit at officer as claimed, judge says

In a 30-page written decision on Friday, the judge found Haworth needed to spit after he began to bleed from the first punch — which Lema said was unjustified — but had intentionally spat toward the back of the police car, away from the officer.

Lema accepted that Lindsay feared a blood-spitting attack but said that belief "was not anchored in reality."

The judge said the risk could have been controlled by keeping Haworth pressed up against the cruiser.

Throughout the hour-long decision, Haworth's mother wiped tears from her eyes.

Lindsay had no visible reaction as he was found guilty.

Both Crown and defence lawyers had called use of force experts who gave opinions on the violent arrest.

The expert for the prosecution — an officer from Edmonton — testified the force used during the arrest was not justified and, in his opinion, was excessive.

Defence expert and former colleague of Lindsay's testified the officer on trial had "unintentionally lost control" when he slammed Haworth's head off the pavement.

Despite police attempts to interview Haworth, he was never able to remember the incident.

Haworth died of a drug overdose several months later.

In his notes taken shortly after the incident, Lindsay never mentioned the three punches to Haworth's head which happened right before the takedown.

Prosecutor John Baharustani suggested Lindsay omitted those details because he had no idea the library camera had caught the violent arrest, an allegation the officer denied.

Lindsay is currently suspended with pay from the Calgary Police Service.

A date for sentencing will be set in the next two weeks.