Federal authorities are investigating three senior navy intelligence officials as part of a probe into an alleged contracting scheme that charged the military $1.6 million for homemade firearms silencers that cost only $8,000 to make, court records show.

The three civilian officials, who oversee highly classified programs, arranged for a hot-rod auto mechanic in California to build a specially ordered batch of unmarked and untraceable rifle silencers and sell them to the navy at more than 200 times what they cost to manufacture, according to court documents filed by federal prosecutors.

The purpose of the silencers remains a mystery. According to the court papers, one of the intelligence officials told a witness in the case that the silencers were intended for SEAL Team 6, the elite commando unit that killed Osama bin Laden.