PIERRE, S.D. (AP) — Newly unsealed documents in the fraud case of a South Dakota man linked to an admitted Russian covert agent show he obtained at least $2.3 million from 78 people for bogus investments dating to at least 1997.

Paul Erickson has pleaded not guilty to 11 counts of wire fraud and money laundering. Authorities say he promised returns of up to 150 percent while spending the money on personal expenses such as motels, flights and college tuition for Maria Butina, Erickson's former girlfriend.

An affidavit unsealed Monday shows that Erickson came to the attention of the FBI in 2016, over alleged fraudulent investments in the North Dakota oil patch.

Butina pleaded guilty in December to trying to infiltrate conservative political groups as a Kremlin secret agent.

Erickson's attorney, Clint Sargent, did not immediately return a phone message.