A man in Denver who fatally shot his wife on Monday may have ingested pot candy and painkillers before the shooting, NBCNews.com reported.

Kristine Kirk, 44, was on the phone with a 911 dispatcher for 12 to 13 minutes after her husband, Richard, began "talking about the end of the world," a probable cause statement said. Shortly before authorities arrived, a gunshot was heard on the call.

Once police got to their house, they discovered Kristine Kirk dead with a gunshot wound to the head. Richard Kirk, 47, now faces first-degree murder charges, NBCNews.com said.

On Thursday, a search warrant affidavit said Richard Kirk claimed to have eaten marijuana candy. Additionally, his wife told the dispatcher he may have had prescription pain medication too, "totally hallucinating" and scaring her and their children.

At the beginning of the 911 call, Kristine Kirk told the operator there was a gun in the home but mentioned it was locked in a safe. However, she began screaming later on when saw her husband go towards the safe.

According to NBC News, police arrived 15 minutes after the call was made -- prompting an investigation into the response time of the officers.

Police said three hours before the incident, Richard Kirk purchased "Karma Kandy Orange Ginger," edible marijuana candy, and "Pre 98 Bubba Kush Pre-Roll," a pre-rolled marijuana cigarette, from a medical/recreational marijuana dispenser in Denver.

Investigators took a blood sample to see what what in his system, but have not made the records public yet. However, the warrant states he "appeared to be under the influence of some type of controlled substance and/or prescription pill" based on speech and pupil size.

Detectives also said he was "rambling to himself" in the back of the police car following his arrest.