Federal agents are trying to determine how a suspected Ohio white supremacist with a felony conviction for manslaughter acquired a cache of 18 assault weapons and other firearms, along with high-capacity magazines and more than 40,000 rounds of ammunition, according to federal law enforcement officials and court documents reviewed by NBC News.

According to the documents, FBI agents who searched Schmidt’s sporting goods store and four trailers behind it, found a  stash of weapons that included AR-15 assault rifles, Ruger and Sig Sauer semi-automatic pistols,  bulletproof  body armor and high-capacity magazines as well as ammunition.

The agents also discovered evidence of Schmidt’s ties to the neo-Nazi movement, documents show. Among the evidence seized, according to search warrants, was a video of a national convention of the neo-Nazi National Socialist Movement; bumper stickers of the National Alliance party, another neo-Nazi group; a “Jewish 500” list -- a supposed roster of Jewish-owned businesses -- and paraphernalia from the “Waffen SS,” Adolph Hitler’s Nazi military force in Germany from the early 1930s through World War II, according to the search warrants.

A federal law enforcement official, who spoke with NBC News on condition of anonymity, said that FBI counterterrorism agents involved in the  case  had picked up evidence that Schmidt  may have been planning attacks against Jewish and civil rights groups in the Detroit area. “This is an active investigation,” said another federal law enforcement official when asked if Schmidt was believed to have been working with any others in the neo-Nazi movement.