This story has been updated with Tony Timpa's mother's response to Dallas Police Association President's statement.
DALLAS (CBSDFW.COM) - Two years ago, 32-year-old Tony Timpa was afraid and called 911 for help.
Less than an hour later, he died in police custody.
To this day, the circumstances of Timpa's death largely remain a mystery.
Last December, three Dallas police officers - Sgt. Kevin Mansell, Officer Danny Vasquez and Officer Dustin Dillard - were indicted on misdemeanor deadly conduct charges in connection to Timpa's death.
The officers are accused of restraining Timpa in a way that led to his death.
The Dallas County District Attorney has not prosecuted the cases and, at the request of the DA, the U.S. Department of Justice is now taking a look at the case.
Much of what took place in the hour from when Timpa called 911 and when he died in the custody of Dallas police was captured on video by the officers' body cameras. The video has not been released to the public.
"He was expecting someone to help him that's why he called," said Timpa's mother, Vicki. "He wasn't expecting several police to kill him."
Timpa was an executive with a convertible living in downtown Dallas high-rise.
His mother said life was good for her son but added he also had his struggles.
Vicki Timpa said her son for years battled addiction to alcohol and drugs.
On the August 2016 night when Timpa called 911, cocaine was in his system, according to the Dallas County Medical Examiner.
Police records state Timpa was acting erratic. He ran out of an adult video store walking right into the middle of traffic on Mockingbird Lane.
Two security guards then restrained him and put him in handcuffs.
What took place next is where the real mystery begins.
Whenever a person dies in police custody in Texas, law enforcement agencies are required to submit a Custodial Death Report to the Texas Attorney General's Office.
According to Timpa's Custodial Death Report, when officers arrived "they attempted to gain control" of Timpa.
Nothing more in mentioned in the report until paramedics arrived.
Timpa was "placed in the ambulance, then he stopped breathing".
Vicki Timpa, Tony's mother, said she believes the police department purposely left out several details in the report.
"They can't tell the truth," she said. "The detectives lied repeatedly to me."
A lawsuit filed by the family claims officers "recklessly" and "knowingly" killed Timpa.
According to the suit, video from officers' body cameras shows Officer Dustin Dillard putting his knee into the back of Timpa for 14 minutes.
Timpa was handcuffed with his face buried in the ground.
The suit claims Timpa could not breathe repeatedly telling the officers, "You're going to kill me".
Timpa then goes completely unresponsive, according to the suit.
Dillard is then allegedly heard on his body camera saying, "I hope I didn't kill him".
Timpa's death certificate lists the cause of death as "sudden cardiac death" caused from "the toxic effects of cocaine and physiological stress associated with physical restraint."
"My son was murdered," Vicki Timpa said.
But Dallas Police Association President Michael Mata said the officers followed department policy and their actions had nothing to do with Timpa's death.
"My heart goes out to his mother," Mata said. "I would hate to lose a child but what killed that man was 20 years of drug abuse."
Vicki Timpa told CBS 11 later that Mata's statement that her son used drugs for 20 years is an "absurd falsehood."
Mata said the Dallas County District Attorney's Office tainted the grand jury that indicted the officers by allowing Vicki Timpa to speak to them.
It is not uncommon for a character witnesses to give a statement to the grand jury but Mata said it is wrong.
"When you have a grieving mother in front of you testifying to their child, of course, there are going to be feelings involved," Mata explained. "But there's not supposed to be feelings involved in a grand jury. It's supposed to be about facts.
Mata said the charges against the officers should be dropped and believes that will be the conclusion the U.S. Department of Justice reaches at the end of its investigation.
The Dallas County District Attorney's Office does not comment on ongoing cases and neither does the U.S. Department of Justice.
The three Dallas officers have been on paid administrative leave for the past two years.
This is the lawsuit filed by Timpa's family against the Dallas police officers:
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