The five family members were found in an Abington condominium complex at about 7:30 a.m. by a relative who showed up to take the children to school, Plymouth District Attorney Timothy Cruz said at a news conference.
“It’s a crime, a crime occurred in that building. Three little children are gone forever,” said Cruz, who also noted it appears they died of gunshot wounds.
He said there is no threat to the public but would not elaborate further on what happened, saying it’s still under investigation.
The children were a boy and a girl who were 9-year-old twins and an 11-year-old girl. The woman was 40 and the man was 43. Cruz did not release their names and said there were no other people in the condo unit.
Abington police Chief David Majenski said there was no history of domestic issues with the family.
The children attended Abington Public Schools, Superintendent Peter Schafer said in a message to parents that was shared with the media.
He called the deaths an “unexpected and unexplainably tragic loss.”
“Their presence touched so many lives and there are no words to express the sadness we feel,” he said of the family.
Counselors have been made available to students, he said.
Abington, a town of about 16,000 people, is about 20 miles (30 kilometers) south of Boston.