Investigators are trying to determine why Broomfield, Colo., police shot and killed a mentally distraught man even though his family told 911 dispatchers he was carrying a gun that shoots plastic pellets, not a real gun.

An independent interagency review team was looking into the circumstances surrounding the June 28 shooting of 21-year-old Kyle Miller. The team will present its findings to the Adams and Broomfield County District Attorney’s Office, which will decide whether charges should be filed against police.

“It’s not real,” the victim’s brother, Alex Miller, is heard telling the dispatcher on the 911 recording.

The dispatcher assures him that “officers are trained in this type of thing. They’re not going to go around shooting people, OK?”

Moments later, Miller was shot to death on a Broomfield street.

Details of the 911 call and the fatal shooting were first reported by The Broomfield Enterprise. Miller’s younger brother had called 911 to report a disturbance at the family’s house.

“My brother is having a breakdown, a meltdown,” he tells the dispatcher.

The Millers’ mother, Cheryl Miller, can be heard screaming in the background as Alex tells the dispatcher his brother tried to cut himself with a pocketknife and also has an Airsoft gun – an imitation gun that shoots plastic pellets.

He says his brother has run away from the house and down the street.

“Is there any way you can let them know he’s got the gun in his hand?” Alex says.

Asked if his brother still has the Airsoft gun in his hand, Alex replies: “It’s not real.”

The dispatcher responds: “I know. I understand. Well, listen, the officers are trained in this type of thing. They’re not going to go around shooting people, OK? And they understand the situation here. So, um, we just want to keep everybody safe.”

The dispatcher later says: “The first thing they’re going to do is get Kyle under control so that he’s safe and everybody else is safe …”

A short time later, another woman calls 911 to report that a police officer has stopped a citizen at gunpoint on a Broomfield street and that another officer is arriving. Kyle Miller was shot after allegedly pointing the Airsoft gun at officers.

Cheryl Miller told the Daily Camera her son was then shot multiple times.

Reached by msnbc.com on Monday, Cheryl Miller said the shooting “has been a very traumatic thing” and the family was awaiting details of the investigation before commenting further.

“We do want to share what went wrong,” she said. “We know they knew it was not a gun and our house had been flagged for a mentally ill person.”

﻿﻿﻿Krista Flannigan, a spokeswoman for the Adams and Broomfield County District Attorney's Office, said Monday it's not known yet when the independent investigation will be completed.

More content from msnbc.com and NBC News:

Follow US News on msnbc.com on Twitter and Facebook