A Colorado Springs man gave his intoxicated ex-girlfriend morphine to help her sleep, accidentally killing her, court records say.

Lee Keyser, 67, was arrested Tuesday on suspicion of manslaughter, months after he told police he gave Donna Mount one of his prescription morphine pills and a tranquilizer, diazepam. He wanted her to settle down, he told police, according to his arrest affidavit. She had been complaining that she was unable to sleep.

Keyser lived with Mount, 52, and her boyfriend, on Adams Drive. Both men told police she had been drinking heavily in the days before her death on April 6.

Police arrested Keyser after a toxicology report revealed Mount’s cause of death was the deadly combination of alcohol and morphine.

Keyser is expected in court July 10.