The suspect, an Oklahoma City man, is accused of mailing hoax letters with white powder and treason warnings.

A man from the midwestern United States is facing federal charges after allegedly mailing hundreds of suspicious letters containing white powder and menacing warnings about treason ahead of the US midterm elections.

On Tuesday, Robin Patrick Martin, a 67-year-old Oklahoma City man, appeared for the first time in a US district court after his arrest a day earlier.

His charges include conveying false or misleading information or hoaxes, as well as mailing threatening communications.

Prosecutors have accused Martin of sending more than 700 letters containing a white powder to hundreds of state and federal officials, including members of the US Congress and election pollsters.

Initial testing showed the white powder was nonhazardous, consisting of yeast or flour, though not all the letters have been fully tested yet.

In an affidavit, Federal Bureau of Investigation (FBI) agent David Cole described the letters as expressing grievances about election integrity.

“The writer of the letter described perceived issues with the 2020 election, claimed that President Donald Trump won the 2020 election, and voiced concerns regarding some of the same issues recurring in the then-upcoming 2024 election,” said Cole.

The letters reportedly warned their recipients that they could face arrest for treason “or worse”.

“Stay on the right side of history! Your life may depend on it,” one letter read, in ink only visible through ultraviolet light, according to the FBI.

Trump, a Republican, has repeatedly cited false claims of election rigging to argue that he — not Democrat Joe Biden —  won the 2020 presidential election.

Those false claims helped spur Trump’s supporters to storm the US Capitol on January 6, 2021, to disrupt the certification of the voting results.

Since being re-elected in 2024, Trump has continued to use his platform to spread fears of election fraud, which is considered exceedingly rare in the US.

The investigation that led to Martin’s arrest stretched back to 2024, when election officials in multiple states reported receiving mail containing a white substance.

The letters included a return address for the fictional “United States Traitor Elimination Army”, in Takoma Park, Maryland.

The FBI has said it gathered video footage of Martin visiting US Postal Service locations in Oklahoma City, Dallas and San Antonio, Texas, to send the mailings.

It also claims it has his fingerprints on a letter addressed to FBI Director Kash Patel.

The Democratic Socialists of America (DSA) reportedly participated in the investigation, after a suspect the FBI believes to be Martin sent messages to the group’s mailing list.

Those messages echoed the mailed letters, calling the DSA’s members traitors and accusing them of treason for voting in Tuesday’s midterm election.