Three people were found dead in their Massachusetts home over prolonged gas exposure, state authorities said Tuesday. 

The police and fire department went to the home, located in Nahant, which is a small town over 10 miles northeast of Boston, to “conduct a wellbeing check” Monday morning, CBS Boston reported. 

The three adults, all related, were found dead inside the home, Massachusetts State Police spokesperson Dave Procopio said in a statement.

The suspected cause of death is “apparent carbon monoxide poisoning,” finding elevated levels of carbon monoxide in the home, according to Procopio. 

“At this point the investigation suggests the cause to be accidental,” Procopio said. 

The family’s neighbor, Ted Mahoney, said Tuesday morning that their deaths were “shocking.” 

"It's hard to believe. I just brought a Christmas present over to them on Christmas, It's in the back door. I don't know when they passed away, but I haven't seen them in a few days," Mahoney told the local CBS affiliate. "Wonderful people, completely wonderful. You wouldn't get better people, just wonderful.”

The Massachusetts Department of Fire Services posted a video on Facebook early Tuesday morning reminding the community of “how important it is to have working CO alarms on every level of your home. They are the only way to detect this silent killer,” in reference to the three deaths. 

All law enforcement agencies involved, including  Massachusetts State Police and Nahant Police Department have differed all inquiry to the Essex County District Attorney’s Office.

USA TODAY has reached out to the Essex County District Attorney’s Office for additional information.

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