Richard Kirk, 47, was being held without bail, facing charges of first-degree murder after allegedly shooting his wife in the head Thursday.
During her 13-minute frantic call to 911, waiting for police, his wife, Kristine Kirk, told the operator her husband "had taken some marijuana and possibly some prescription medication for back pain."
She said he was "totally hallucinating" and she feared for her and their three children's lives.
During Richard Kirk's arrest, police believed he was under the influence of a controlled substance "based upon his speech patterns, his inability to focus and his pupil," a search warrant affidavit said.
Police said they also found a receipt in the Kirk home for a purchase of marijuana-laced candy.
A blood sample will be examined to determine if Richard Kirk was under the influence.
Meanwhile, police said they are investigating whether the time it took to respond to Kristine Kirk's 911 call was reasonable.
"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.