RALEIGH, N.C. -- An appeals court gave new hope yesterday to the defense of a former Green Beret doctor convicted in the 1970 murders of his wife and daughters, ruling that his lawyers can introduce evidence that a prosecutor threatened a witness.
A panel of the US Court of Appeals for the Fourth Circuit in, Richmond, granted a motion by Jeffrey MacDonald's lawyers to present the new evidence in Raleigh federal court. It could result in a new trial, said Hart Miles, one of MacDonald's lawyers.
''I think it's the biggest development in the case since the trial," Miles said.
The defense filed the motion last month, after a former deputy US marshal came forward last year to say he heard a defense witness tell a prosecutor she was in the MacDonald home in Fort Bragg, N.C., on the night of the slayings.
Jimmy B. Britt, part of the security detail during MacDonald's 1979 trial, said he heard prosecutor James Blackburn tell Helena Stoeckley that he would indict her for murder if she told the same story on the witness stand. Stoeckley later testified she could not remember where she was the night of the slayings.
Blackburn, who has denied making the remark, did not immediately return a call yesterday seeking comment.
''She never told us she was there," Blackburn told reporters last month. ''I don't know why this man is coming forward 25 years later. I don't know what his motivation is, but he's simply mistaken."
MacDonald's wife, Kathryn, said she and her husband were ''just overwhelmed" with the news, which she gave him in a telephone call yesterday afternoon to the federal prison in Maryland.
''It's astonishing, wonderful," she said from her home in Columbia, Md. ''It's given me back my faith that truth means something -- truth means everything -- and I know Jeff feels the same."
Lead lawyer Tim Junkin said MacDonald's team will ask the federal court to vacate the conviction.
MacDonald, whose case was dramatized in the best-selling book and TV miniseries ''Fatal Vision," responded to the ruling in a statement posted on a website devoted to exonerating him.
''We are grateful for the court's fair and thoughtful consideration, and are exhilarated that we will now be able to present all the evidence amassed since trial that demonstrates actual innocence," MacDonald said in the statement.
MacDonald, 62, is serving three consecutive life sentences in a federal prison for the murders of Colette MacDonald, 26, and their daughters, Kimberley, 5, and Kristen, 2. He has argued that intruders killed his family in an attack that left him seriously injured.
According to MacDonald, one of the attackers was a woman with a long, blond wig and floppy hat. He said he heard her say: ''Acid is groovy. Kill the pigs." Stoeckley, who died in 1983, fit the description, according to court papers.
Britt, now 67, said in an affidavit that he kept quiet for more than 25 years out of a sense of duty to the people he worked with, but the secret eventually became too much to bear.