The boy had called 911 Tuesday evening to report shots fired at his Burlington home in eastern Colorado home and that at least three people had bee shot, said Steve Johnson of the Colorado Bureau of Investigation.
When officers arrived, they found the bodies of 50-year-old Charles Long and his wife, 51-year-old Marilyn Long. Two of their children were wounded -- a 5-year-old girl and a 9-year-old boy.
It was unclear whether the 12-year-old suffered any injuries.
Johnson said there are no other suspects, and there's no reason to believe there's a continuing risk to the community of about 3,700 near the Kansas border.
Less than 24 hours after the shootings, friends gathered for a candlelight vigil Wednesday evening on the sidewalk in front of the family's house on a corner lot.
They said the Long children were homeschooled and the family was deeply religious, attending one neighborhood church on Saturdays and another on Sundays.
"You'd always see them around town, volunteering for stuff," said Ronnie Speakman, who was at the vigil with about six other people who said they knew the family. "He worked for Frito-Lay and you would always see him stacking chips in the aisle, always a smile on his face."
Two blocks away at the Evangelical Free Church, which the family attended, Pastor Ron Lee told more than 100 people at a prayer service that the gathering was meant as an opportunity for prayer and encouragement while members grieve.
"Most of it is confusion," Lee said. "I don't understand exactly what's gone on or why. Some of the reports that have come out, I'm not sure I even believe it."
Lee, church members and friends described the family as longtime residents and active members of the church, with Charles serving as an elder and Marilyn serving as director of the church's children's ministry.
The Longs had seven children, ranging in age from their mid-20s to 5, and the younger children were home schooled by Marilyn Long. One church member, rancher Paul Rhoades, 74, said Marilyn Long grew up in Burlington and attended high school with his daughter.
Lee said the injured children were Sarah, 5, and Ethan, 9. Greg James, an elder at the church, said he visited the family -- including older siblings and the children's grandmother -- at The Children's Hospital in suburban Denver and visited the children as they recovered in the hospital. He told the congregation that the family was hopeful the children would recover.
Lee said the Longs' 12-year-old son was involved with church activities, including handing out church bulletins and greeting visitors before Sunday service, working with audio and video equipment, running Powerpoint presentations and helping children learn memory verses.
Lee said the boy missed church on Sunday because of a conflict with a school activity but that he called the church to make sure there was a substitute greeter.
"He was pleasant, helpful, a good spirit, a good kid," Lee said. "I'm so shocked. I almost feel like I need to hear from him or one of the children. He's not your typical 12-year-old."
Lee said there weren't any changes in jobs, housing, or schooling that the family talked about or any outward signs that might give a clue to what happened.