True crime? Errol Morris reexamines the evidence

AP Photo/Lennox McLendon
Former Green Beret officer Dr. Jeffrey MacDonald, center, leaves Terminal Island prison escorted by federal marshalls, Aug. 22, 1980. MacDonald was convicted on charges he murdered his pregnant wife and two daughters.

Last Updated 11:59 a.m. ET

(CBS News) In the annals of modern-day crime and punishment, few cases have been more gruesome - or more controversial - than that of convicted murderer Jeffrey MacDonald. Gruesome - and and now, after many years, controversial all over again. Our Cover Story is reported by Rita Braver:

It was one of the most sensational murders of its time. In the early morning hours of February 17, 1970, at Fort Bragg, N.C., Colette MacDonald - four months pregnant - and her daughters, Kimberly, age 5, and Kristen, age 2, were savagely beaten and stabbed to death.

Husband and father Jeffrey MacDonald was severely injured as well, with 19 puncture wounds.

MacDonald told a bizarre story: Three young men and a woman had attacked the family for no apparent reason. But suspicion quickly focused on Jeffrey MacDonald - a handsome, Princeton-educated Green Beret Captain and emergency room physician.

MacDonald has always said he is innocent. But he was convicted and given multiple life sentences - a story detailed in the 1984 NBC miniseries "Fatal Vision."

It was based on the book by Joe McGinniss, and left little doubt that Jeffrey MacDonald had killed his family without remorse.

And yet . . .

"I believe him to be innocent," said documentary filmmaker Errol Morris. "Because no one has ever showed me any kind of convincing argument for his guilt. They just simply have not."

The fact that this man has taken up MacDonald's cause is significant. Morris - director of such films as "The Fog of War," and a winner of the MacArthur "genius" grant - is someone known for challenging what appears to be truth.

"Once you create a story, a narrative, and let's say it's a compelling narrative - it may not be a true narrative, but it's a believable narrative - it may be difficult or impossible to shed it,' Morris said. "What happens when all the fingers are really pointing at you saying, 'You're guilty, you're guilty, you're guilty, you're guilty, you're guilty'?"

Morris knows all about that. His 1988 film, "The Thin Blue Line," is credited with helping free Randall Dale Adams, a man who was wrongly convicted of murdering a police officer.

Morris even got Adams' accuser to confess he'd framed an innocent man.

"It seems like you just have this passion for maybe going after stories that are hard," said Braver. "This is not easy work."

"I like hard stories," Morris replied. "I like digging. Maybe I'm one of those people that's always turning over a rock and looking at what's underneath."

He turned his lens on the powerful . . . in "The Fog of War," his Oscar-winning portrait of Vietnam-era Defense Secretary Robert McNamara . . . and he embraced the oddball, in his provocative examination of pet cemeteries, "Gates of Heaven."

If Morris courts the image of an eccentric, don't be fooled. He is the hard-driving director of commercials - over a thousand - for everything from Miller Beer to Nike shoes.

He uses his profits to fund projects dear to his heart, like his multi-year study of the MacDonald case, now a 500-page book, "A Wilderness of Error."

"This is a story where the defense was forced to play with a deck of cards where most of the cards had been withheld, and it was just simply unfair," he said.