A federal grand jury indicted an undocumented immigrant living in St. Louis, Mo., on charges that he committed voter and tax fraud as part of an elaborate stolen identity theft scheme, the Department of Justice announced Wednesday.

Kevin Kunlay Williams, a Nigerian citizen, is suspected of illegally reentering the United States under a false name in 1999 after he was deported four years earlier.

Williams later registered to vote in federal, state, and local elections in 2012 by claiming he was an American citizen. He is suspected to have voted in both the 2012 and 2016 presidential elections, according to the indictment.

Federal authorities also suspect that Williams stole the identities of several public school employees from a payroll company, subsequently using the IDs to file more than 2,000 fraudulent federal tax returns that sought more than $12 million. The Nigerian man also allegedly stole Electronic Filing Identification Numbers (EFINs) to print refund checks, directing the IRS to send the refunds to prepaid debit cards.

Upon his arrest in January, federal authorities said Williams was illegally in possession of a firearm. Williams faces up to 20 years in prison if convicted of mail fraud, aggravated identity theft, voter fraud, illegal reentry, and being a felon in possession of a firearm, according to the indictment.

President Donald Trump in February ordered Vice President Mike Pence to lead an investigation into reports of widespread voter fraud during the 2016 election, but the probe has yet to take off.