Stoeckley died in 1983. But in 2006, Jimmy Britt, a former U.S. deputy marshal at the trial, who died in 2008, swore in an affidavit that he heard a prosecutor threaten Stoeckley before she testified. MacDonald's lawyer said that's crucial information.
"It is definitely serious prosecutorial misconduct if, in fact, the prosecutor threatened a defense witness," said Hart Miles, one of MacDonald's lawyers.
Miles also pointed to a 2007 affidavit from Stoeckley's mother who said that shortly before Helena died, she told her mother she was there in the house the night of the murders.
MacDonald's lawyers assert that new DNA evidence from the crime scene, which was tested in 2006, will show that MacDonald is innocent, after all.
"There was a hair found under the fingernail of Kristen MacDonald, Jeffrey MacDonald's youngest daughter, and DNA testing showed that was an unsourced hair, that it did not match Jeffrey MacDonald or anybody else in his family," Miles said. "Our position is that it corroborates the story that he's told from the very beginning, that there were intruders in that house."
The government's theory was that MacDonald had "got into a fight with his pregnant wife because his youngest daughter, Kristen, had wet the bed; that he picked up a club to strike his wife and accidentally struck and killed his daughter, Kimberley, who was trying to intervene; and that then, in order to cover up his accidental misdeed, killed his wife and then mutilated and killed his youngest daughter and tried to make it look like a cult slaying," court papers said.
MacDonald's blood, along with fibers from his torn pajamas, were found on and under the victims' bodies. No DNA evidence, fingerprints or fibers from Helena Stoeckley were found anywhere in the house.
Prosecutors have never wavered.
"I don't believe Jeffrey MacDonald will ever admit to killing his family," said Jim Blackburn, the prosecutor during the trial. "He is not going to live forever and there is going to come a time, if you believe in this sort of thing, when he's going to be able to see Colette and Kimberley and Kristen again, and the question he's going to have to answer to them and the question I would ask of Jeffrey MacDonald is: Was it all worth it?"
Kathryn MacDonald believes the prosecution's case is crumbling.
"If the only way to get a conviction was to hide anything that didn't fit with the prosecution's theory, they did a good job at the time. But now it's all unraveling. Please, please, a neutral party, look at this evidence as a whole. And that is the law, look at it as a whole. And our government doesn't want that," she said. "I hate all this, I can't wait for it all to be gone and life to start anew."
A ruling on whether or not MacDonald will get an appeal is expected in the coming weeks.