Prosecutors have asked a court to officially close the case of a man accused of fatally shooting a guard at the U.S. Holocaust Museum.

James Wenneker Von Brunn, a white supremacist, died in January; a court filing Wednesday asks that the federal case against him be closed.

The filing says that a medical examiner provided Von Brunn's certificate of death and that he died naturally but as a result of a variety of medical conditions.