SACO — A family of five, including three children ranging in age from 4 to 12 years old, were found shot to death Sunday inside a southern Maine apartment, authorities said.

Investigators said a gun was found near one of the bodies and it appeared no one outside the family was responsible for the shootings.

State police Sgt. Chris Harriman said murder-suicide is one of the scenarios being investigated but that determination will be made by the state medical examiner’s office.

Authorities did not release the names of the family but said the parents were in their 30s and the children were ages 4, 7 and 12.

Neighbors Heather and Dellas Nason stopped to place flowers on the ground outside the apartment building, which was surrounded by crime scene tape. Heather Nason said she used to baby-sit the children.

“I still don’t want to believe it,” she said. “I love those children like they were my own.”

Their father was a maintenance worker for the complex who was friendly and outgoing, neighbors said.

“You’d walk by and he’d ask how your day was going. He was really nice,” said neighbor Kristi Harkins. She said she had seen the eldest boy playing outside on Saturday.

Investigators said a family friend had contacted a worker at the apartment complex worried about the well-being of the family. The worker entered the apartment and discovered one body, then immediately called police.

Detectives said they believed the shootings happened around 11:30 p.m. Saturday.

Saco police found the bodies in bedrooms. Police described the firearm found in the apartment as a long gun. Shell casings were also recovered.

Neighbors described the complex along the Saco River as a friendly and safe place where kids rode bicycles and played together. But the droves of children who usually circle the complex were all inside Sunday night, replaced by concerned adults.

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