"Fatal Vision" murder convict Jeffrey MacDonald hopes DNA evidence will clear him

(CBS News) Jeffrey MacDonald's lawyers are going back to court over DNA evidence in the so-called "Fatal Vision" murders.

MacDonald has served 30 years for the killings of his wife and two young daughters. The former Green Beret doctor has always maintained his innocence. And he wants one more chance to get out of prison.

Timeline of events in the Jeffrey MacDonald case
"48 Hours": Jeffrey MacDonald: Time For Truth

MacDonald insists that a group of drug-crazed hippies invaded his home in Fort Bragg, N.C., on February 17, 1970, that they attacked him and savagely stabbed his wife Collette, and their two daughters, Kimberly, 5, and Kristen, 2.

He recounted the story to CBS News' "48 Hours" in 2007, saying, "I heard a female voice say, 'Acid is groovy. Kill the pigs.'"

The brutal crimes - just months after the murders committed by Charles Manson and his followers - became a national sensation and even led to a best-selling book and NBC mini-series, "Fatal Vision."

MacDonald has been in prison since 1982, serving three life terms for the murders. But a new book by acclaimed filmmaker and author Errol Morris says MacDonald was telling the truth all along.

Morris - whose 1988 movie "The Thin Blue Line" helped win freedom for a man wrongfully convicted of murdering a police officer - told Rita Braver of "CBS Sunday Morning" that DNA evidence not available at the time of MacDonald's trial now points to his innocence.

"Sunday Morning": True crime? Errol Morris reexamines the evidence

Morris said, "They did find hair under the fingernails of one of the girls that could not be sourced to anybody in the house."

And it wasn't MacDonald's, Morris said.

Morris also said MacDonald's story is supported by Helena Stoeckly, who repeatedly confessed to being in the house with her drug-using friends the night of the murders.

Stoeckly said in a 1982 interview with CBS News, "I walked into the master bedroom (while MacDonald was unconscious). ... Collette was sleeping on the bed."

But during MacDonald's trial, Stoeckly suddenly couldn't remember many of the details of that night, and Morris said he knows why. "The prosecutor threatened her and told her essentially to change her story, or he would indict her for murder," Morris told "CBS This Morning."

MacDonald faces an uphill legal battle and prosecutors still believe they got the right guy. But MacDonald remains hopeful he will be released someday. He told "48 Hours," "There's a legitimate possibility that I will be winning this case."

Watch Anna Werner's full report in the video above.