Five members of a family, including three children, were found shot dead at their southern Maine home on Sunday, with a gun located near one of the bodies and no outside involvement suspected, a police spokesman said, according to The Associated Press.

The five family members: a father and mother in their 30s and three children believed to be 4, 7 and 12, were discovered on Sunday afternoon in three rooms of their second-floor apartment in Saco, about 17 miles southwest of Portland, state police spokesman Stephen McCausland said, the AP reported.

They were found by a person affiliated with the management company that runs the apartment building where they lived, after a family friend expressed concern about their well-being, according to the AP. The worker entered the apartment and discovered one body, then immediately called police.

Police were still notifying next of kin and did not expect to release the identities of the victims before Monday, McCausland said, the AP reported. A detective said murder-suicide was one of the scenarios being investigated.

Investigators said it appeared no one outside the family was responsible for the shootings and were planning to release the identities on Monday, according to the AP.

Police said the bodies were found in three bedrooms and described the firearm found in the apartment as a long gun, the AP reported. Shell casings also were recovered.

Neighbors described the father as well known in the apartment complex along the Saco River because he was one of the maintenance workers, according to the AP.

They described a friendly family with a 4-year-old girl and boys aged 7 and 12 who were part of a group of neighborhood kids who constantly rode their bikes or played tag and other games in a community that residents described as safe, the AP reported. The parents were in their 30s.

"The kids were great. They were just happy kids, and it's just a huge shock," said Nason, who with her husband Dellas placed flowers outside the apartment on Sunday, according to the AP. As for the parents, "they'd take the shirt off their back for you," she said.

Police believe the shootings happened at about 11:30 p.m. Saturday, based on reports from neighbors about loud noises coming from the apartment, the AP reported. The neighbors didn't contact police.

State and local police, along with the medical examiner, were at the scene Sunday night, according to the AP. Officials said autopsies were scheduled for Monday.