MacDonald is serving three life sentences for the 1970 murders of his pregnant wife, Colette, and their daughters, Kimberley and Kristen in what is now known as the "Fatal Vision" case. The case was the basis of a book with the same title.
As the hearing for the former green beret continued Tuesday morning, first on the stand was the former wife of Deputy US Marshall Jim Britt, who died four years ago.
During MacDonald's 1979 trial, Britt was assigned to go to South Carolina to pick up a potential witness -- Helena Stoeckley.
Stoeckley was an alleged drug addict from Fayetteville who told Britt she was involved in the MacDonald murders, according to the testimony of Britt's wife.
She told the judge that Britt said Stoeckley, "described that apartment to a 'T.' She even described a broken hobby horse that was there."
Her testimony backed up MacDonald's story that drug-crazed hippies had come into his family's Fayetteville home while he slept on a couch. MacDonald said they fatally stabbed and beat his pregnant wife and two daughters, then stabbed him and left him for dead.
Before he died, Britt told one of MacDonald's attorneys that a federal prosecutor had threatened to charge Stoeckley with murder to keep her from testifying.
Following that testimony, MacDonald's attorney called Stoeckley's brother to the stand.
He testified that as MacDonald's 1979 trial was starting, the FBI called his parents and told them to, "keep Helena under control and keep her mouth shut and out of the case."
Stoeckley died in 1983. Her brother also said on the stand that while Stoeckley was fatally ill, she confided in their mother that she was present the night of the murders.
Testimony is expected to last about two weeks.