A couple who are both school bus drivers with ties to the Michigan Militia embezzled at least $50,000 from the woman's mother and used it to buy an arsenal of firearms that included a machine gun and 17,000 rounds of ammunition, authorities say.

Sarah Nick, 32, and her 33-year-old husband, Steven Nick, embezzled the money from Sarah Nick's 67-year-old mother, who has serious health problems, Genesee County Sheriff Robert Pickell said at a news conference Tuesday at which he displayed the weapons.

The investigation started in November because of suspicions of possible elder abuse, The Flint Journal (http://bit.ly/1ahvQkS ) reported. Pickell said authorities got a search warrant for the couple's Davison Township home and found 30 firearms and the ammunition in a basement bunker.

Investigators also found multiple bulletproof vests, one of which has a patch that said, "We kill for peace."

The couple were arrested March 27. They were freed on bond and are due back in court in Flint on Thursday for a hearing. They have no lawyers on record with the court who could comment on the allegations and do not have a listed phone number.

Most of the weapons are legal, but one AR-15 assault rifle had an illegally short barrel, Pickell said.

"It's an issue because they were purchased with stolen money," Pickell said.

Pickell said the Nicks have ties to the Southeast Michigan Volunteer Militia. On its website, the group says its goals are "defending against disaster, crime, invasion, terrorism and tyranny."

Sarah Nick had worked for a company that provides buses for the Flint School District, said district spokeswoman Lisa Ermak. She said the company fired Sarah Nick. Pickell said Steven Nick was a driver for the Davison Community Schools.

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Information from: The Flint Journal, http://www.mlive.com/flint