Muhammad, already convicted and sentenced to death for one of the sniper killings, was to have faced trial beginning in January in the analyst's death, one of 10 killings that terrorized the Washington area over three weeks in October 2002.
But Circuit Judge M. Langhorne Keith said Muhammad's trial in the slaying of Linda Franklin did not begin within the time limit set by Virginia law, which requires a trial within five months of a person's arrest unless the defendant waives the right.
"I find that the defendant's statutory right to a speedy trial was violated," Keith wrote. "The statutory mandate was not met because a trial was not commenced in the Circuit Court of Fairfax within five months."
Prosecutors and defense attorneys disagreed on when Muhammad was arrested.
Fairfax County Commonwealth's Attorney Robert F. Horan Jr. did not immediately return a telephone message left by The Associated Press.
One of Muhammad's attorneys said the defense was mindful of shooting victims as they pursued the appeal. "It needs saying that we well remember the victims in these cases and the families who suffered so greatly," attorney Jonathan Shapiro said.
Muhammad was already convicted and sentenced to death last year for the Oct. 9, 2002, murder of Dean Harold Meyers in neighboring Prince William County. But Fairfax County authorities sought a second conviction in case the first were overturned on appeal.
Muhammad's teenage accomplice, Lee Boyd Malvo, was convicted last year in the Franklin killing and sentenced to life in prison.
Ironically, nearby Montgomery County, Md., is to mark the second anniversary of the deadly sniper shootings Saturday by dedicating a memorial to the victims.
The crack of a sniper's rifle outside a Wheaton supermarket on October 2, 2002, began the three-week rampage that left ten dead and three hurt and terrorized the Washington D.C, area. Six of the dead lived in Montgomery County.