Javon Martin, 25, was arrested and charged with robbery and murder in the first degree. A jury trial has been scheduled for April 23, according to court records.
Martin is one of two people charged in the case. His cousin, 20 year-old Roger K. Clark III, pleaded guilty to first-degree murder in this case earlier this month. His sentencing is set for April.
Diener, 57, was found stabbed to death on his way to work at an Arlington fitness center in December 2009.
Clark was originally arrested in June of last year, but charges against him were dropped in October. It's unclear why the charges were dropped, Arlington Now reported.