U.S. District Court documents allege Army Spc. Christopher N. Lanum, 25, was wearing the costume when he attempted to cut Spc. Mitchell Stone's throat at U.S. Army base in Newport News, Va., The Northern Virginia Daily said Friday.
FBI Special Agent Jennifer V. Collins alleges in a federal court affidavit that Lanum's girlfriend, Pasty Ann Marie Montowski, was likely also involved in Sunday's attack.
Collins has called for Montowski to be charged as an accessory after the fact in relation to the attack. Stone survived the attack and was airlifted to a nearby hospital for treatment.
Meanwhile, Lanum and Montowski fled the military base in a minivan and drove at high speeds until crashing into a pickup with law enforcement officers in pursuit, Collins alleged. After the crash, officers alleged Lanum was seen brandishing a shotgun and they were forced to open fire.
Virginia State Police spokeswoman Corinne Geller told The Army Times that a full investigation was under way into the shooting that left Lanum dead.