An Andover, Massachusetts father, mother and their 12-year-old son were shot dead at their home early Thursday morning, authorities said as they opened an investigation into the killings.

In a press conference around 8:30 a.m., Essex District Attorney Paul F. Tucker did not release the names of the family members killed, nor did he say who was suspected in the shootings. But he stressed to local community members that there was “no danger at all to anyone in the public.”

The 12-year-old boy was a sixth-grade student at St. John’s Preparatory School in Danvers, Tucker said. The school has canceled classes Thursday, a message on its website said.

Andover Police Chief Patrick Keefe said the father was 56 years old and the mother was 55.

Around 3:20 a.m., police received a 911 call from inside the home, at 48 Porter Road, Keefe said. He did not specify who made the call.

Responding officers forced two doors open to enter the home, where they found the bodies of three family members, Keefe said.

When officials addressed reporters Thursday morning, Keefe said the investigation was in its initial stages.

“Obviously, we know the how,” he said. “We’re trying to figure out the why right now.”

Tucker told members of the public to seek help if they were facing mental health struggles. He also thanked the police, firefighters and medical professionals who responded to the Andover home.

“We’re always concerned about their wellbeing,” Tucker said. “These men and women do an extraordinary job under some very difficult circumstances.”