The Johnsons, however, do not accept those findings. Their attorneys say authorities may have covered up evidence that someone killed the teenager. A grim post-mortem photo of his swollen, distorted face has been posted by the family on protest signs and websites to help rally support for reopening the investigation.
"My family won't be satisfied until someone is behind bars and someone is convicted for what happened," says Kenneth Johnson, pacing the sidewalk one Friday afternoon as his wife sat with her sister and mother. "Going over it with common sense, how can it be an accident?"
He's not alone in wondering. Last month, about 200 people joined Johnson's family outside the Georgia Capitol in Atlanta for a rally calling for answers. The gathering was billed as: "Who Killed K.J.?"
Word has spread through social media, with one Facebook page — "R.I.P. Kendrick Johnson" — drawing more than 25,000 followers. The Florida attorney who represented Trayvon Martin's family took up the Johnsons' cause in October, drawing more attention to the case. Now the U.S. attorney for middle Georgia is conducting a formal review.
Perhaps it's the bizarre manner in which the teenager was found dead that leaves some disbelieving. Or lingering doubts about how police in the South treat cases involving black victims. Or that a grieving family simply cannot come to terms with a tragic loss.
Johnson's supporters won't let his case be put to rest. But is there evidence someone killed him?
It was the morning of Jan. 11, 2013, at Lowndes High School, a sprawling campus attended by 3,000 students near the Georgia-Florida state line. Philip Pieplow's gym class was filling out a survey. Some students sat on the bleachers in the school gymnasium, while others climbed atop a cluster of 21 wrestling and cheerleading mats standing three-deep against a wall.
The rolled-up mats stood just over 6 feet high, each measuring nearly 3 feet across. Soon students who had clambered on top of them began yelling for help. A pair of feet clad in socks could be seen inside the center hole of one mat.
"I reached (and) grabbed one of his ankles hoping for a response," Pieplow said in a written statement included in the investigative file on Kendrick's death. "There was none, and I knew he was lifeless at that point."
Students began calling 911 and, within minutes, police and paramedics arrived.
At the same time, Jacquelyn Johnson was at the school asking if her son had shown up for class, guidance counselor Dana Hutchinson later told investigators. Kendrick hadn't come home the night before.
The youngest of four children, Kendrick grew up in Valdosta, one of the largest cities in rural south Georgia. His grandmother affectionately called him her "peculiar grandchild," because he tended to be quieter than his brothers and sisters.
A junior at Lowndes High, Kendrick made average grades but had a knack for numbers. He kept accounts in his head of his allowances, his father says, and saved cash in stashes throughout his bedroom.
He also liked sports, having played 8th-grade basketball and football and track when he started high school. After taking a year off from team sports, Kendrick was working toward rejoining the football team, his father says.
Matthew Mark Carron, an 18-year-old former football teammate who was among the students investigators interviewed, remembered Kendrick once got into a fight with another player before a game. Carron told investigators it was the only negative thing he could remember about Kendrick.