(CNN) -- A Denver woman called 911 when her husband began to hallucinate and speak of "the end of the world."
For 13 minutes, the wife spoke of fear -- for herself, their three scared children, her husband.
Richard Kirk wanted his wife to shoot him, she told 911.
She screamed when he went to the family safe and grabbed a gun.
The 911 operator heard what sounded like a gunshot. The wife went silent on the 911 call.
Responding police found her dead Monday in the family home with an apparent gunshot wound to the head, authorities said. She was identified as Kristine Kirk by CNN affiliate KWGN.
Kirk admitted that he killed his wife -- "without questioning," a police document says -- when an officer put him in the backseat of a patrol car, the probable cause document says.
Those harrowing events, provided by authorities, are now being investigated by Denver police, who are looking at how 911 handled the 13-minute emergency call and whether Kirk was using marijuana or another drug, authorities said Wednesday.
"This is under investigation," Denver police spokeswoman Raquel Lopez said about the possibility of marijuana use.
Colorado became the first state in the nation to legalize the sale of recreational marijuana, allowing pot stores to open for business on January 1.
At a court hearing Wednesday, Kirk, 47, was ordered held without bail on an accusation of first-degree murder, Denver court records showed.
In response to questions about the incident, Denver police posted on its Twitter page: "We will report the truth, even if mistakes were made."
In response to apparent questions about the handling of the 911 call, the police posted another tweet: "No indication the call taker erred. Very tough call to handle, please give benefit of doubt."
The city of Denver auditor's office this year began studying police response times, which have grown longer in recent years, the Denver Post reported. The report is expected in June, and police have cited fewer officers and limited budgets for hiring more officers since 2008 as causes for longer response times, the newspaper reported.
Lance Kirk, brother of Richard Kirk, told KWGN that he was stunned to hear of the incident.
"I know that wasn't Richard -- let's just say that," Lance Kirk told the news outlet. "I hope there are some answers that come out about this.
"My heart goes out to those three boys and Kris' family -- mom, dad, sister and brothers," Lance Kirk added, referring to his sister-in-law. "This is a terrible thing."
Neighbors, family and friends told the station they knew the couple as loving and devoted parents.
"Whatever those boys are going through right now, my thoughts and my prayers are with them, and I hope that they find peace," neighbor Kristin Fynewever told the affiliate.
Other neighbors told CNN affiliate KCNC that the couple's three young sons are all in grade school.
"I used to go to school with them and they were really nice kids and they didn't deserve for this to happen to their mom and their dad," neighbor Alesa Moskal told KCNC.
CNN's Mariano Castillo, Stefan Simons, Kara Devlin and Dottie Evans contributed to this report.