Four people were discovered dead at a New York City home on Friday in what is being investigated as possible carbon monoxide poisoning, The New York Times reported.

The victims, two men and two women all age 70 and above, were declared dead at the scene Friday afternoon by firefighters who received a call about "hazardous materials" at a residence in Queens. A relative placed the call after entering the home to "check up on" the residents, police told the newspaper.

Police said two of the victims were 83-year-old Jerry Hugel and his 80-year-old wife Marie, the parents of a sergeant in the New York Police Department. The third victim, Gloria Greco, 70, was a tenant and the fourth, Walter Von Thadden, 76, was a friend of the couple's.

Jerry Hugel was found dead near a running car inside a garage attached to the house, the Associated Press reported. His wife Marie Hugel was found in a kitchen in the basement.

The friend was found dead in the living room on the first floor, and the tenant was also found on the first floor, police said.

Reports later revealed it was the couple's son, 30-year police veteran Robert Hugel, who discovered his parents dead when he went to check on them.

"He could not get in touch with his parents, so he went over there to the house," police told The NY Times. "It does not appear to be criminal. It appears to be accidental at this point. It's a shame."

Carbon monoxide, which is colorless and has no smell, is also suspected in the deaths of a father and his seven children found Monday at their Maryland home. A generator in the home was out of gas.

"Something like this is a wake-up call," Myrna Dominicci, the Hugels' neighbor, told The NY Times.

"They're the nicest people you're going to meet, I'm so sorry that this happened to them."