DALLAS — It wasn't an emergency call, but rather a mother's request for help like she had done before.

But there's nothing routine about what happened seconds after Shirley Harrison opened the door to her South Oak Cliff home on June 14, 2014. All of it was captured on a Dallas policeman's body camera.

"Oh, he's just off the chain. You can hear him," Harrison said to two responding police officers.

Her son Jason stood casually behind her. The 38-year-old man — who is bipolar and schizophrenic, she said — twirled a screwdriver in his hands as his mother walked out of the home ahead of him.

Video: Watch the Dallas PD video

Jason did not appear threatening, but as soon as officers noticed the potential weapon, they yelled at him to drop it.

Police said he lunged forward at them, causing them to draw their pistols and start shooting. Jason Harrison collapsed against his garage door with at least three gunshot wounds as his mother began wailing, the video showed.

"When you're dealing with somebody who is mentally ill, you're not supposed to agitate! You're not supposed to move fast! You're not supposed to inflame!," said Geoff Henley, Harrison family's attorney.

Should police have reacted differently?

"The officer has literally less than about three seconds to react to this situation," said Keith Wenzel, a tactical trainer for law enforcement agencies.

Jason Harrison's family is suing the two Dallas officers for violating his civil rights and wrongful death. They acquired the body cam video as part of the legal proceedings, and wanted the public to see how police handled a mentally ill man.

For a quarter of a century, Wenzel has taught tactics to police officers. In this situation, he said there wasn't enough time to use a baton, and the police were too close to use a TASER.

"Let's just say he did move back," explained Wenzel. "Well, if the suspect advances on the mother and stabs her, well people would say the officer should have stood between the mother and the son — which is what he did."

The shooting shows limitations of body cams. The camera in this case was unable to capture much after the officer drew his firearm.

The lesson learned, Wenzel said, is how quickly a situation can escalate.

But Harrison's family hopes a judgment against officers also teaches police to react differently when dealing with the mentally ill.

Both Dallas officers involved in this incident — John Rogers and Andrew Hutchins — have since returned to active duty.

Their attorneys said the shooting was justified.

Dallas Police said it has turned over all evidence to the Dallas County District Attorney's Office to investigate.