A family of five, including three children, was shot and killed inside their home in southern Maine on Saturday, in what authorities believe could be a murder-suicide.

The bodies were discovered a day later on Sunday afternoon, and according to state police, cited by USA Today, "all indications are that no one outside of the family was responsible for the deaths." Authorities also said that a gun had been recovered from near one of the bodies. The names of the family members -- a father and mother in their 30s and the children aged 4, 7 and 12 -- will be released Monday.

State police spokesman Stephen McCausland reportedly said that the bodies had been discovered after a worried family friend contacted a person associated with the management of the apartment complex. The two-storey apartment is located in Saco, about 10 miles southwest of Portland.

"I still don't want to believe it," Heather Nason, a neighbor, who used to sometimes baby-sit the children, said, according to Associated Press, or AP. "I love those children like they were my own."

Investigators reportedly believed that the family was shot on Saturday. Officials also reportedly said that the autopsies are scheduled for Monday.

"You'd walk by and he'd ask how your day was going. He was really nice," neighbor Kristi Harkins reportedly said, adding that she had seen the eldest boy of the family playing outside on Saturday.