Like many teenagers, Marc Smerling wanted to see a horror film.

But the movie –it may have been a Halloween re-release, he said – was sold out. Instead, he saw The Thin Blue Line, Errol Morris' distinctive, 1988 documentary about a murder case.

"It blew me away," Smerling recently told the Television Critics Association (TCA). He savored "the visual storytelling, the sort of courage it took to make something that incredible."

Now, decades later, he's working with that filmmaker. A Wilderness of Error (debuting at 8 p.m. ET, Friday, on FX) is directed by Smerling; Morris wrote it, adapting his own book.

This is another true-crime tale, yet different: Thin Blue Line is about a case few people had heard of; Wilderness focuses on Dr. Jeffrey MacDonald, who drew intense interest throughout the 1970s.

"It is about so many people with so many diverse, conflicting opinions," Morris said. There's "evidence that almost seems to prove a case, but never actually does."

When Thin Blue Line opened in 1988, Morris was 40, known mainly for Gates of Heaven, a 1978 film about a pet cemetery.

It's good that Smerling saw Thin Blue Line because it needed the money. It only made $1.2 million at the box office; Halloween made that much its first weekend and ended with $70 million.

But Thin Blue Line had other impacts. It helped free a man who'd been convicted of murder. It made top-10 lists and was added to the National Film Registry.

And its style became popular. "I just thought it changed documentaries," Smerling said.

Morris made other documentaries, winning a 2004 Academy Award for The Fog of War: Eleven Lessons from the Life of Robert S. McNamara. He also made commercials and, in recent years, wrote articles and books; his Wilderness of Error book drew Smerling, who has an Emmy for The Jinx: The Life and Deaths of Robert Durst.
 
Wilderness goes back 50 years, to when MacDonald, an Army doctor, phoned for help. Military police arrived and found his wife and daughters brutally murdered and MacDonald with lesser wounds.

The Army held a hearing, dismissed charges, and gave him an honorable discharge. His late wife's father kept pushing to clear MacDonald's name; he dug into the case – and switched his opinion.

That, Morris said, "is extraordinarily interesting – the fact that he went from vigorously defending Jeffrey to being one of his principal accusers." In 1974, he spurred a grand jury investigation. Five years later, MacDonald went on trial; he's been in prison ever since.

That father-in-law became the centerpiece of Fatal Vision, a two-part mini-series based on Joe McGinniss' book. Karl Malden won an Emmy for his fierce portrait.

This became the accepted view until Morris re-opened the whole thing.

MacDonald had talked about four hippies, one a young woman in a floppy hat. A police detective soon found Helena Stoeckley, who said she'd been high at the time, but thought she'd been there. Stoeckley would tell people that several times before her death (at 32) 15 years later. Considered an unreliable witness, she was barred from testifying.

"People look at evidence," Morris said. "If the evidence squares with what they want to believe, they accept it. If it does not, they reject it."

That's what keeps stirring true-crime arguments and fueling true-crime filmmakers.