Dr. Jeffrey MacDonald, 69, is serving three life terms in federal prison. The former Army surgeon, assigned to the Special Forces, still pleads innocent and heads to court on August 20.

This past week lawyers for the U.S. government have rejected a request by Jeffrey MacDonald to depose nine witnesses prior to his August trial date, citing it too costly and unnecesary.

MacDonald was convicted in 1979 for the murders of his pregnant wife and two daughters in February 1970.

In April 2011, The Fourth Circuit Court of Appeals issued a ruling, remanding the case to federal district court. The three-judge panel found that James C. Fox, a federal judge in Raleigh, improperly refused to consider DNA evidence and witness statements in a recent attempt by MacDonald to win exoneration.

Hoping for a new trial for MacDonald, his lawyers are pushing for a new trial by asking for new DNA evidence to be conduted. Nine witnesses are listed on the U.S. District Court according to the Fayetteville Observer's report last Wednesday.

One of the names on the list is Lee Tart. He is a retired U.S. marshal who was a close friend of Jim Britt, a now-deceased former marshal.

In 2011 new evidence was presented from Jim Britt. Britt claimed to have heard Blackburn threaten Helena Stoeckley, a woman MacDonald claims was wearing a blond wig inside his house on the night of the murders.

Britt claimed Stoeckley admitted to being in the MacDonald house the night of the murders. After Blackburn threatened to charge her with the slayings, however, she testified she couldn't recall where she was that night. Britt and Stoeckley have since died.