For 13 minutes, a terrified Denver woman told a 911 dispatcher on the telephone that her husband was hallucinating, talking about the end of the world and asking her to shoot him. Their three small boys were scared.

Then, when she realized her husband had retrieved a gun from a safe, she began to scream. A gunshot ended her call for help.

By the time officers arrived late Monday, 44-year-old Kristine A. Kirk had died from a gunshot wound to her head.

Police arrested Richard Kirk, 47, on suspicion of first-degree murder, said Sonny Jackson, a Denver police spokesman. Kirk told police he killed his wife, according to a probable-cause statement in the case.

Denver police said Tuesday they are investigating whether the husband used marijuana before the shooting. Police are also investigating their response to the 911 call.

“Any time a person dies while communicating with Denver’s emergency services, we examine the circumstances to ensure that the incident was handled properly and we look for areas to improve upon,” the department said in a news release.

News of the shooting stunned the University of Denver neighborhood where the family lives in a tidy brick Tudor home.

“They’re a great family with great kids,” said Lily Weiner, who has lived across the street from the family’s house for eight years. “All of this just doesn’t make sense.”

Weiner stopped to place flowers on the steps of the family’s home.

“She was beautiful,” Weiner said. “She was a great mom.”

Photos: Woman found dead in home near University of Denver

The incident unfolded about 9:30 p.m. Monday when the victim called police to her home in the 2100 block of South St. Paul Street.

Kristine Kirk told the dispatcher her husband was “talking about the end of the world and he wanted her to shoot him,” according to the probable-cause statement.

Kristine Kirk told the dispatcher there was a gun in the home but that “it was in a safe,” the court document said. But then she said he had the gun in his hands.

Kristine Kirk then screamed over the phone until a single shot was fired, according to the statement. Jackson said Kristine Kirk was on the phone with a 911 operator for about 13 minutes.

Read: Probable cause statement of Richard Kirk

The call initially came through as a domestic disturbance, Jackson said, but the longer it went on the more alarming it became for authorities.

Police response times in Denver have continued to lengthen in recent years.

Chief Robert White has cited fewer officers and budget constraints that have kept the city from hiring officers since 2008 as a cause for the increasing response times.

Officers arrived on the scene shortly after the shooting.

“They were almost there,” Jackson said. “We will look into the call and see if the time line is appropriate.”

The Denver auditor’s office launched a study this year to examine police response times. Auditors examined multiple factors that may be the cause of the increase in response times, said spokesman Denis Berckefeldt.

The audit is expected to be finalized in June.

The Denver Police Department and the city’s Combined Communications Center is investigating the incident response.

Jackson would not say whether a gun or drugs were recovered from the home.

“We are looking at marijuana as a possible part of the investigation,” he said.

Prior to Monday’s shooting, Kirk did not have a felony criminal record in the state, according to the Colorado Bureau of Investigation database. He was arrested in 2000 in Douglas County, on suspicion of driving under the influence.

A front porch light was on at the home Tuesday morning, as investigators streamed in and out, carrying evidence boxes. A silver SUV with DU hockey stickers on the back window was parked in the driveway.

James Slater, a neighbor who was driving to the gym, stopped at the home around 7 a.m. and asked what was happening. When he was told, he was stunned, and his eyes began to well up.

Slater turned and walked a short distance away, went down into a crouch and put his hands to his face. He recovered moments later, stood up and called his wife on his cell phone.

“This is just incredible,” Slater said moments later.

Slater said he knows the family and that his son, an elementary school student, plays soccer with one of the family’s three boys. Slater said he saw the family Saturday at a youth soccer game.

“It was just a normal day,” Slater said. “It’s just hard to believe.”

Slater described the family as popular in the Observatory Park neighborhood.

“Everybody knows them,” Slater said.

Richard Kirk was described by neighbors as friendly, someone who always waved to those who were coming and going on the busy block. His boys were often seen playing around the house, neighbors said.

Twelve-year-old Alesa Moskal said she was not close with the three children, but had attended school with them.

Moskal and her mother, Jenny, dropped flowers by the home Tuesday afternoon.

“I bet there is going to be a lot of sadness in this neighborhood and my old school,” she said. “I remember them being very nice kids.”

Staff reporter Jordan Steffen contributed to this report.