DALLAS (CBSDFW.COM) – For nearly three years, Vicki Timpa said her nightmare had been kept away of the public’s eye.

That changed this week with the public release of body camera footage showing her son’s 2016 death while in Dallas police custody.

The police body camera footage shows Tony Timpa, 32, being restrained by Dallas officers and yelling, “You’re gonna kill me!”

At a news conference Friday, Vicki Timpa said, “It’s really hard to hear my son scream ‘help me’ and cry. They laugh at him and they torture him and they killed him and they have fun doing it.”

Timpa’s death came less than an hour after he called 911, saying he was off his medication for schizophrenia.

The video shows officers pinning Timpa to the ground with his hands cuffed behind him for nearly 14 minutes

On the video, officers are heard mocking Timpa, with one yelling “Tony, time for school. Wake up.”

Timpa’s mother said hearing the officers mock her son was the hardest part of the video to watch.

“They started making jokes because it was fun for them,” she said.

It was only when the officers loaded Timpa onto a stretcher did they question whether he was alive.

The Dallas County Medical Examiner ruled Timpa’s death a homicide, listing the cause as sudden cardiac death from cocaine and the physiological stress associated with physical restraint.

Deadly conduct charges against the officers involved were dismissed earlier this year.

The Timpa family has filed a civil lawsuit claiming excessive force with the officers “recklessly” and “knowingly” killing Timpa.