(CNN) -- Kenneth Johnson never believed.
When his son, Kendrick, was found with his body headfirst in a rolled-up gym mat at Lowndes County High School in south Georgia, authorities offered their take on what happened: The 17-year-old had been reaching for his sneaker when he got caught up in it, then suffocated to death. In other words, it was all a tragic accident.
"When he came up this cockamamie story of how they found Kendrick," the late student's father said Friday of the local sheriff, "... right there, from the beginning, we had no reason to trust them at all.
"Because they didn't show us justice."
Ten months after burying their son, the Johnson family says that's all they're looking for -- justice. Not to declare his case closed, as the Lowndes County Sheriff's Office did after a Georgia Bureau of Investigation autopsy found that Kendrick died of position asphyxia.
The Johnson's skepticism led them not to give up, but to push on with their own investigation. A second autopsy conducted by a private pathologist, at the request of Kendrick's parents, found he died because of "unexplained, apparent non-accidental blunt force trauma."
There have been more questions since then, including why their son's body and skull were stuffed with newspaper before his burial.
The pursuit of getting answers has made the pain of losing a son -- a boy they described as jovial, polite and good-hearted -- a little more bearable.
"Just to know that we're fighting for Kendrick is what gets me up in the morning," his mother, Jacquelyn Johnson, told CNN's Anderson Cooper on Friday night.
"We know we've got to fight a little harder every day."
Conflicting determinations of what happened
A loving son and brother, a three-sport athlete who never got in trouble with the law, a jokester who made every day fun, a gentleman with good manners and a sunny disposition.
That was Kendrick Johnson, in a nutshell, his parents say.
"Every parent all over the world would want to have a son like Kendrick," Kenneth Johnson told CNN's Cooper. "Kendrick was a great boy."
On January 11, he was in the gymnasium of Lowndes County High in Valdosta. A few still images, taken from surveillance cameras, are perhaps the last of Kendrick Johnson alive. They show him walking across the bare floor with no one else in sight, though it's quite possible that other, unreleased pictures would show Kendrick wasn't alone.
The next pictures of the teenager are far more horrifying: His body, clad in jeans and layered orange and white T-shirts, is wedged in the wrestling mat. His face is bloated with pooled blood, some of which poured out of his body and soaked his dreadlocks and spilled onto the floor.
There were more streaks of blood on a nearby wall. But it wasn't Kendrick's, investigators say.
In fact, the Georgia Bureau of Investigation told CNN on Thursday that DNA tests to try to determine whose blood that was found no match. Lt. Stryde Jones, from the sheriff's office, told CNN in May that the blood looked like it had "been there for an extended period of time."
A pair of orange-and-black gym shoes are found a few yards from the teen's body. They had a substance that looked like blood, though investigators told CNN that it was not -- which is why the shoes weren't collected for potential evidence. Nor was a hooded sweatshirt a few feet away.
"I don't believe this was an accident," said Harold Copus, an Atlanta private investigator who looked at the death scene imagery. "I think this young man met with foul play."
And Dr. Bill Anderson, the private pathologist hired by Johnson's family who conducted the second autopsy, found that Johnson had a blow to right side of his neck "consistent with inflicted injury."
"I've never had a case that I can recall where the prosecution actually was told that this may well be a homicide -- the prosecution being the state, the police and so forth -- and then they didn't bother prosecuting," said Anderson, from Forensic Dimensions in Heathrow, Florida. "It's mystifying."
Yet a number of official reports paint a different picture.
A January 25 report by the Valdosta-Lowndes County Regional Crime Laboratory cited "no signs of blunt force trauma on Johnson's face or body."
And the original autopsy results released by the Georgia Bureau of Investigation May 2 identified "no significant injuries."
Mother: We'll keep at it 'until we get justice'
So what is the truth?
The Johnson family says one way to find out is through a coroner's inquest, a process in which a panel -- after reviewing evidence and testimony -- decides on a cause of death. They plan to file a lawsuit as early as next week to force the district attorney to force such an inquest.
If this process ends with a ruling Kendrick Johnson's death was a homicide, not an accident, then authorities would logically reopen their investigation. And with that, the Johnsons hope, they'll find out who is responsible.
Maybe then they'll see the full surveillance footage from the school gymnasium that winter day, which might show whether anyone else was there with Kendrick Johnson.
And maybe they'll find out who stuffed newspaper in place of the teenager's internal organs. GBI spokeswoman Sherry Lang said the organs were placed in Johnson's body before it was sent to a funeral home. The funeral home's owner, Antonio Harrington, wrote to the family that his firm never received the teen's organs, claiming they were "discarded by the prosecutor."
Jacquelyn Johnson says the family is committed to keeping Kendrick's spirit alive.
They held a party this week to mark what would have been his 18th birthday. And Jacquelyn Johnson says she still talks to him, up in heaven, to "tell him that I love him and I missed him."
Asked why she does, the mother said, "It just gives me more motivation to keep fighting for him -- until we get justice."
CNN's Victor Blackwell contributed to this report.