A 24-year-old Montville man pleaded guilty Tuesday in U.S. District Court to supplying heroin with fentanyl to a woman who died from an overdose on May 31, 2016.

James Butler, who has been detained since his arrest on Jan. 31, faces up to 20 years in prison when he is sentenced July 12 by U.S. District Judge Alvin W. Thompson.

According to the office of U.S. Attorney Deirdre M. Daly, members of the Montville Police Department who were called to an apartment on Route 32 found a deceased 34-year-old woman lying face down on the bathroom floor.

The state Office of the Chief Medical Examiner ruled the cause of the unidentified woman's death was acute ethanol and fentanyl intoxication. The investigation revealed that Butler had supplied the heroin with fentanyl to the woman.

Butler is being prosecuted as part of an ongoing statewide initiative targeting narcotics dealers who distribute heroin, fentanyl or opioids that cause death or serious injury to users. Daly said at a news conference in Middletown on Tuesday that her office has investigated over 120 overdose deaths and prosecuted more than 60 cases.

The investigation is being conducted by the Drug Enforcement Administration, Connecticut State Police, Groton Police Department, Montville Police Department, New London Police Department, Statewide Narcotics Task Force – East, and the Regional Community Enhancement Task Force.

Assistant U.S. Attorney Douglas P. Morabito is prosecuting the case.