If John Mark Byers were a rich man, you might think he had bought his way out of trouble. But Mr. Byers, as he would be the first to tell you, is just plain folks. An apparently uneducated, overalls-wearing Arkansan who once owned a small jewelry store, he is the reason HBO's documentary ''Paradise Lost 2: Revelations'' is so horrifying and fascinating. It is also as disturbing as a film can be.

At the end of the original HBO film ''Paradise Lost: The Child Murders at Robin Hood Hills'' three teenagers were in prison, convicted of the 1993 murders of three 8-year-old boys. One of the teenagers, a 19-year-old, was on death row. But everything in the film had begun to point toward Mr. Byers, the stepfather of one of the murder victims.

That was 1994. Many viewers, learning that a sequel has been made, may expect it to be the story of how the young men were exonerated and the real murderer or murderers arrested. It is not.

In the beginning ''Revelations'' looks as if it will follow the pattern of another real-life case, that of Hurricane Carter as seen in the film ''The Hurricane.'' A group of young people became convinced of Mr. Carter's innocence and devoted themselves to winning him a new trial and getting him out of prison. Happily, it worked.

In the case of the three young men convicted in Arkansas -- Damien Echols (then 19, now 24), Jason Baldwin (now 21) and Jessie Misskelley Jr. (23) -- a similar support group springs up. But when these advocates come to Jonesboro, Ark., bearing ''Free the West Memphis Three'' T-shirts, they appear to be greeted with the same warmth that met early civil rights workers arriving in the South.

The fact that some are from faraway states like Ohio, New Jersey and California is not in their favor. There may be a knee-jerk reaction to the term ''West Memphis Three,'' reminiscent of the 1960's radical left.

Or perhaps local residents suspect the group of being a cult. As a teenager Mr. Echols believed in Wicca, a religion that worships nature and advocates a kind of benevolent witchcraft. The prosecutors decided that the murders (in which one of the victims was sexually mutilated) had been ritualistic, committed by devil worshipers; they equated Wicca, and the fact that Mr. Echols was a fan of the rock group Metallica, with Satanism.

Interviewed for the sequel, the chief investigator for the original trial says he is sure the young men in prison are the murderers. For one thing, Mr. Misskelley confessed.

Even local television personalities seem convinced of the young men's guilt. When Burk Sauls, a leader of the support group, says on the air that Mr. Misskelley's confession was coerced, a man at the KAIT anchor desk says skeptically, ''What was coercive about it?'' It doesn't help that Mr. Sauls, who often seems to be smirking, answers with a reference to ''a time line problem'' instead of reiterating that Mr. Misskelley was questioned for hours. And when Mr. Misskelley did finally agree with the police officers who were saying he did it, he told them that the murders were committed at noon (when the victims were still at school). Mr. Misskelley has an I.Q. of 72.

The most amazing part of the sequel concerns bite mark evidence. When the defense, with the support group's help, brings in a criminal profiler, he looks at photographs of the crime and sees bite marks that were either overlooked or ignored during the first trial. The three men in prison give bite impressions for analysis; none match. The prosecution and the defense bring in dueling odontologists. One says yes, these are bite marks; the other says they are not. The judge decides the prosecution odontologist is telling the truth.

As for Mr. Byers, he now has false teeth. But, he says, he has had them since before the murders. Then he says his teeth were knocked out in a fight. Then he says he lost his teeth because of peridontal disease. According to the film, dental records show that an oral surgeon removed Mr. Byers's teeth in April 1997, almost four years after the murders.

In the course of the film Mr. Byers takes a polygraph test with questions about the murders. The man who conducts the test tells him that he appears to be telling the truth about these matters ''as far as you see them.'' (Mr. Byers turns to the camera and declares himself vindicated, those last six words apparently not having registered with him.) It is established that Mr. Byers has a brain tumor and is taking several medications.

More than once Mr. Byers kneels beside a grave and speaks to the deceased. In the first film it was his son's grave. In ''Revelations'' it is that of his wife, Melissa, who died in 1996 of an undetermined cause. ''I know your heart was broken,'' he says as the camera rolls. ''I know you couldn't stand the death of your child. But oh God, I wish you hadn't left me.'' The impression is of a very bad actor imitating grief. If Mr. Byers is indeed innocent, he is doing himself no favors with these performances.

Mr. Byers was arrested last June for selling prescription drugs to an undercover narcotics agent. Sentenced to eight years, he could be paroled in October. Meanwhile Damien Echols is still on death row. He could be executed by lethal injection as early as May. Hearings for his last possible appeal on the state level end on Sunday.

AMERICA UNDERCOVER
Paradise Lost 2: Revelations
HBO, tonight at 10

A film by Joe Berlinger and Bruce Sinofsky. For HBO: Sheila Nevins, executive producer; Nancy Abraham, supervising producer.

Published: 03 - 13 - 2000 , Late Edition - Final , Section E , Column 4 , Page 6