Jeffrey MacDonald, a clean-cut Green Beret and doctor convicted of killing of his pregnant wife and their two daughters, is getting another chance to try proving his innocence -- more than four decades after the nation was gripped by his tales of Charles Manson-like hippies doped up on acid slaughtering his family.

The case now hinges on something that wasn't available when he was first put on trial: DNA evidence. A federal judge planned to hold a hearing Monday to consider new DNA evidence and witness testimony that MacDonald and his supporters say will finally clear him of a crime that became the basis of Joe McGinniss' best-selling book "Fatal Vision" and a made-for-TV drama.

It's the latest twist in a case that has been the subject of military and civilian courts, intense legal wrangling and shifting alliances.

"This is Jeff's opportunity to be back in court almost 33 years to the day of his conviction," said Kathryn MacDonald, who married him a decade ago while he has been in prison.

MacDonald, now 68 and not eligible for parole until 2020, has never wavered from his claim that he didn't kill his pregnant wife, Colette, and their two daughters, 5-year-old Kimberley and 2-year-old Kristen. He has maintained that he awoke on their sofa in their home at Fort Bragg in the early morning hours of Feb. 17, 1970, as they were being attacked by three men and a woman.

In an October 2000 letter MacDonald wrote to Kathryn MacDonald, provided by her to The Associated Press, he wrote: "It would be a dishonor to their memory to compromise the truth and `admit' to something I didn't do -- no matter how long it takes."

The gruesome stabbing and beating deaths came just three months after the Manson Family slayings in California were revealed. The pregnant wife and MacDonald's description of the woman attacker chanting "acid is groovy, kill the pigs" all fed into fears that Manson-type killers were on the loose in North Carolina. The word "pig" was written in blood on a headboard -- the same word that was written on the door of pregnant Manson victim Sharon Tate's house in Los Angeles.

The Army charged the Ivy League-educated MacDonald with murder, then dropped the charges months later after an Article 32 hearing. By December 1970, MacDonald was not just a free man but also had received an honorable discharge.

But his father-in-law, Alfred Kassab, who initially believed in his innocence, changed his mind and eventually persuaded prosecutors to pursue the case in civilian court. In 1979, MacDonald was charged, convicted and sentenced to life in prison, a sentence he now serves at the federal prison in Cumberland, Md.

MacDonald has stood by his innocence claim so strongly that he refused to apply for parole for years, and when he did, he refused to acknowledge any guilt and was rejected. MacDonald and his supporters have continued to pursue legal avenues over the years to try to clear his name.

U.S. District Court Judge James Fox will consider two types of evidence: three hairs that don't match the family's DNA and a statement from Jimmy Britt, a deputy U.S. marshal when the case was tried. Britt, who has since died, gave a statement to defense attorneys in 2005 that he heard prosecutor Jim Blackburn threaten Helena Stoeckley, a troubled local woman whom MacDonald had identified as one of the attackers.

A previous MacDonald attorney has said Stoeckley was prepared to testify she was in the MacDonald home the night of the murders until Blackburn threatened to charge her with the slayings. She later testified she couldn't remember where she was that night.