The death of an off-duty Chicago Police Department detective Sunday morning at his Garfield Ridge home on the Southwest Side has been ruled a suicide — the fourth by a CPD officer in the past four months.

The 43-year-old man was found dead shortly after 10 a.m. at his home in the 5700 block of South Nottingham, according to Chicago police and the Cook County medical examiner’s office.

An autopsy Monday found he died of carbon monoxide poisoning inside the garage and his death was ruled a suicide, the medical examiner’s office said.

“We are grief-stricken over the news that an off-duty police detective took his own life this weekend,” CPD spokesman Anthony Guglielmi said in a statement. “From what we know at this early stage this does not appear to be work-related but it is an absolute tragedy for all of us.”

Guglielmi said the detective was a 19-year department veteran. Counselors and chaplains have been assigned to his unit.

“For some time now I have been telling public officials, citizens and media that being a police officer is an extremely stressful job,” Kevin Graham, president of the Chicago chapter of the police union, the Fraternal Order of Police, wrote in a statement.

“It is truly unfortunate that we [lose] good police officers to permanent solutions for a temporary problem,” Graham added. “Our hearts and our prayers go out to his family.”

The detective was the fourth CPD officer to die by suicide since July. Three other officers fatally shot themselves between July and September. Two of them took their own lives in the parking lot of the Calumet District headquarters on the Far South Side.

After the suicide last month, Police Supt. Eddie Johnson urged police to get help when needed in a note to department members.

“Death by suicide is clearly a problem in Law Enforcement and in the Chicago Police Department,” he wrote. “We all have our breaking points, a time of weakness where we feel as if there is no way out, no alternative. But it does not have to end that way. You are NOT alone. Death by suicide is a problem that we can eliminate together.”