One of the three over the weekend was an Arlington resident, reports say.
According to Middlesex District Attorney Gerry Leone, at about 6:40 p.m. on Friday, Cambridge Police responded to a call for shots fired inside a single family home at 161 Grove St., Cambridge.
Upon arriving, officers found three family members had been fatally shot, Leone said.
The Boston Globe identified the victims, according to a relative, as: Patrick Pizzuto, 63, his brother, Robert Pizzuto, 52 and their mother, Mary, 91.
The alleged suspect, John “Jack” Brosnahan, 67, who was a former Bedford Police Officer and resided at the residence on Grove Street, was found dead around 10:30 p.m. at 1400 Soldiers Field Road in Brighton from an apparent self-inflicted gunshot wound.
The DA said that at this time, it was believed Brosnahan shot and killed the three victims, and then shot himself.
— Franklin Tucker contributed to this report.