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CHICAGO — An off-duty Chicago police officer has died from apparent carbon monoxide poisoning on the city’s Northwest Side.

The officer has been identified by the medical examiner as 36-year-old Xu Meng.

Chicago police said Meng and his 29-year-old wife were discovered unresponsive inside of a residence on the 3900 block of West Ainslie Street in Albany Park around 8 p.m. Tuesday.

The two were transported to Swedish Hospital in critical condition, where Meng later died.

His wife is in critical condition but has stabilized at the hospital. Her name has not yet been released.

A large police presence gathered at the hospital. Officers stood at attention and saluted, as the remains of their fallen was loaded into an ambulance.

A procession was held from Swedish to the Cook County Medical Examiner’s office, where an autopsy was performed. The results of that autopsy are pending.

Melissa Rios, a neighbor, said she heard the alarm going off for hours.

 “Around noon, 1 p.m., I started hearing the beeping sound,” she said. “I thought to myself someone must be burning something in the kitchen.”

A source told WGN News a car in the attached garage was found on but out of gas and carbon monoxide levels were 140 parts per million, well into a lethal range.  Police have not confirmed there was a car involved.

The townhome association president David Graubard said neighbors were alerted to the situation later Tuesday evening when Meng’s fellow officers arrived to do a well-being check.

 “The father needed to pick up the child in the afternoon and the police told me he’d been 2-plus hours late to come pick his son up,” Graubard said. “It’s terrible. They’re super nice people. I just saw them this weekend out in front. The kid’s adorable and he was always super friendly.”

Meng has been on the force for 22 months and worked out of the 24th District in Rogers Park. He had received a crime reduction award and an honorable mention over his short CPD career.

Detectives from Area 3 are conducting a death investigation.