The death of Suzanne Morphew, who went missing on Mother's Day in 2020, has been ruled a homicide, according to autopsy results released Monday by the Colorado Bureau of Investigation.

The CBI said the autopsy determined Morphew's cause of death to be "homicide by undetermined means in the setting of butorphanol, azaperone, and medetomidine intoxication."

Butorphanol is a synthetic opioid, which, on its own, is found in a nasal spray used for the treatment of migraines, and can also be used as a painkiller. The butorphanol-azaperone-medetomidine combination is typically used to immobilize wild and captive animals including deer and bears, according to studies archived by the National Institutes of Health's National Library of Medicine.

"The Colorado Bureau of Investigation and our law enforcement partners understand and appreciate the public interest surrounding this case, said CBI Director Chris Schaefer. "The investigative team assembled to work this case continues to follow the evidence and only the evidence as we seek justice for Suzanne's death."

Morphew's disappearance nearly four years ago, when she left home for a bike ride on Mother's Day, made national headlines. Her bicycle was found down a ravine off Chaffee County Road 225, but investigators at the time said it didn't appear to have been involved in a crash, and there was no blood at the scene.

Her husband, Barry Morphew, was considered the prime suspect, and was charged with her murder. The case was dismissed without prejudice in April 2022, before her body was located, meaning charges could again be filed against him.

Morphew's body was located on Sept. 22, 2023, during an unrelated search, in the area of Moffat in Saguache County.

CBI said Morphew's family has been notified of the autopsy results. No additional arrests have been made since her body was found. She left behind two teenage daughters.

-- with reporting by TMX