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A Denver woman who spent nearly 15 frantic minutes on the phone with a 911 dispatcher was killed Monday night by a bullet to the head before help arrived.

The gunshot was the last sound 911 dispatchers heard on their call with Kristine Kirk, 44, which lasted for approximately 12 to 13 minutes, said Denver police officer Raquel Lopez.

Kirk's husband, Richard, 47, was arrested on suspicion of first-degree murder, Lopez said. He appeared in court Wednesday, waived his formal advisement, and will remain in custody.

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In her call to 911, Kirk said her husband was "talking about the end of the world and he wanted her to shoot him," according to a probable cause statement filed in the case. There was a gun in their house, Kirk said at the beginning of the phone call, but it was locked in a safe.

As the call went on, Kirk told the 911 dispatcher that her husband was hallucinating, scaring their three young children, the court document said. Then, when she saw her husband had gone to the safe and gotten the gun, she started screaming. The sound of a single gunshot reverberated on the call, and Kirk wasn't heard from again.

Officers, who had initially been sent to the house on a domestic disturbance call, were dispatched to the Kirks' at about 9:32 p.m. Richard Kirk was arrested at 9:55 p.m.

Denver police are reviewing their response to the incident and investigating what took so long, Lopez said.

When officers arrived, they found Kristine Kirk lying on the floor with an apparent gunshot wound to the head. She was pronounced dead at the scene.

Police are investigating the possibility that Richard Kirk — who admitted to killing his wife on his way to the police station, according to the probable cause statement — took marijuana prior to the shooting.

Police response times have gotten longer in recent years, The Denver Post reported, with the Denver police chief blaming budget constraints that have prevented the city from hiring any new officers since 2008.

An audit from the Denver auditor's office examining police response times is expected to be finalized in June, looking at multiple factors that could be contributing to the long response times, The Denver Post said.

— Elizabeth Chuck