Each weekday, the mother and father come to the same corner outside the county courthouse and spend hours camped out with cardboard signs. As cars stream past, some drivers wave and honk. Others occasionally shout jeers: “Go home!” or “Give it a rest!”

It’s been a year since Kenneth and Jacquelyn Johnson’s son was found dead inside a rolled-up gym mat at his high school — the victim, investigators concluded, of a freak accident. Authorities determined 17-year-old Kendrick Johnson fell head-first while reaching for a shoe and was trapped. Almost a full day passed before his body was discovered.

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 afternoon as his wife sat with her sister and mother. “Going over it with common sense, how can it be an accident?”

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.

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. 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.

Deputies found nothing to dispute the portrait family and friends painted of a well-liked and responsible teenager, says sheriff’s Lt. Stryde Jones, who oversaw the investigation.

Lowndes High School has dozens of security cameras watching over its hallways, entrances and parking lots. Four motion-activated cameras are posted in the gym where Kendrick was last spotted on Jan. 10, 2013.

Surveillance footage shows him entering the gym shortly after 1 p.m. and walking toward the far corner where the mats were stored. It doesn’t capture him leaving, and Kendrick never showed up for his fourth-period weight training class.

Footage released by the Lowndes County Sheriff’s Office fails to show what led to Kendrick’s death.

The Associated Press obtained the 522-page case file through an open records request and reviewed it, along with security camera footage and crime scene and autopsy photographs, for this story.

Three students told deputies that some classmates kept gym shoes stashed behind or beneath the gym mats. One said he and Kendrick shared a pair of Adidas shoes and that after class the student always would “go to the mats, jump up and toss the shoes inside the middle of the hole.”

When Kendrick was found, the Nike shoes he’d worn to school were tucked behind his legs inside the mat. Also on the floor was an Adidas shoe. Deputies found its match pinned beneath Kendrick’s arm and head.

Medical Examiner Maryanne Gaffney-Kraft found no wounds except for a scrape on the back of Kendrick’s right wrist and three small injuries on his right pinky. She determined he died accidentally from “positional asphyxia,” meaning his body was stuck in a position that prevented him from breathing.

Investigators concluded Kendrick fell into the mat while trying to retrieve one of his gym shoes. Nobody saw him struggling or heard him cry out, though a steady stream of students were in and out of the gym until 8 p.m.

The case was closed May 2. But to Kendrick’s family, it remained an unsolved crime.

Kenneth Johnson doesn’t say much when asked why someone might have wanted to kill his son, or who he thinks could have done it.

For those inclined to reject the official findings, the case has its share of stumbles and loose ends to fuel alternate theories.

The lack of camera footage showing Kendrick’s last moments has been seized on by family attorneys, who say they fear the footage was edited as part of a cover-up. Images from the camera pointed toward the gym mats are also blurred. School officials told investigators a basketball had knocked the camera out of focus.

Investigators also waited to call the county coroner until six hours after the body was found, though state law requires immediate notification. It was standard practice in Lowndes County to process potential crime scenes first, but that has since changed, Jones says.

“At best it was incompetence,” says Benjamin Crump, an attorney for the Johnson family. “At worst it was some conspiracy to conceal the truth.”

Kendrick’s parents obtained a court order to exhume their son’s body and hired a private pathologist to perform a second autopsy. Dr. William Anderson reported finding hemorrhaging beneath the skin of Kendrick’s jaw and neck and concluded he suffered a fatal blow near his carotid artery that appeared to be “non-accidental.”

U.S. Attorney Michael Moore in Macon stepped in Oct. 31, announcing his office would review the case. Those findings have not yet been released.

Kenneth Johnson says neither he nor his wife have returned to work since that January day. He is a long-haul trucker, and she a school bus driver.

“I want the world to know what happened to Kendrick,” he says.