Denver District Attorney Mitch Morrissey will not file criminal charges against a police officer who in July shot and killed a mentally ill man wielding a knife in a mobile home park.

The shooting by Officer Michael Traudt was justifiable, Morrissey wrote in a decision released Monday. The victim, Paul Castaway, was violent, potentially suicidal and had an “astounding combination” of alcohol and drugs in his system, the letter said.

Morrissey also released a dramatic video of the shooting as it unfolded inside the Capital City Mobile Home Park on West Kentucky Avenue.

“Castaway’s actions and the statements he made suggest he had decided to die and further decided that Officer Traudt would be the instrument of his demise,” the letter said. “Officer Traudt’s decision to fire his pistol was, under these circumstances, objectively reasonable and appropriate. Indeed, Castaway gave him no other choice.”

Police had been called to the area by Castaway’s mother, who had a protection order against her son, after he burst into her apartment, trashed it and poked her in the throat with a kitchen knife.

Castaway’s mother, who is American Indian, ran for help at the Denver Indian Center on Morrison Road and called police. The two officers saw Castaway walking down the road, and the pursuit began.

In the video, children scatter as two police officers chase Castaway down a lane.

Castaway ran into a small, fenced parking area that was a dead end. He turned back toward the officers and advanced with the knife at his throat.

Traudt and a second police officer, Jerry Lara, stood between Castaway and the children.

The officers told investigators they had ordered Castaway to stop and drop the 7-inch kitchen knife.

Lara put his gun back in his holster and reached for his Taser as Traudt fired three times, striking Castaway twice in his torso.

Witnesses, most of whom were teenagers, told investigators that Castaway had threatened to kill himself.

The shooting once again triggered protests in Denver after several family members, including Castaway’s mother, said police should have found another way to deal with Castaway rather than shoot him.

Morrissey’s critics accuse him of being too cozy with the police and sheriff’s departments to prosecute officers in excessive-force cases.

On Friday, Denver Chief Judge Michael Martinez scolded the district attorney’s office for failing to prosecute a Denver Sheriff Department deputy who slammed a shackled inmate into a courtroom wall.

The deputy should have been charged with misdemeanor assault, but the statute of limitations had expired, Martinez ruled after a five-hour hearing on the case.

David Lane, a Denver lawyer who represents the Castaways, said he will consult with the family now that the letter and video have been released.

“It’s a difficult situation, and we have to weigh all of our options now that we’ve seen the video,” Lane said. “The issue is whether or not less-than-lethal force would have been the appropriate action.”

Traudt has returned to his duties as a patrol officer, said Denver police spokeswoman Raquel Lopez. An administrative review of the case is ongoing.

Noelle Phillips: 303-954-1661, nphillips @denverpost.com or twitter.com/noelle_phillips