A 91-year-old woman and her caretaker were found dead inside a home, where firefighters said there were dangerous levels of carbon monoxide.
The woman and the caretaker, 38, were found dead in the Tyngsborough home on Saturday.
The home was ventilated by firefighters. The police and fire departments and National Grid were on the scene Sunday, looking to identify the cause of the dangerous levels of carbon monoxide.
"This is an absolute tragedy and we will continue to work diligently to determine how this occurred," Tyngsborough Police Chief Richard Howe said in a statement.