An Oklahoma City man was charged with sending hundreds of threatening letters containing white powder to state election officials, lawmakers, pollsters and media organisations ahead of the midterm congressional elections. Robin Martin, 67, was charged in US District Court in Oklahoma with conveying false or misleading information and hoaxes and mailing threatening communications. Testing of powder found in the letters determined it was either harmless yeast or flour, the FBI said in an affidavit. Martin, who was arrested Monday, was ordered temporarily detained Tuesday by a federal magistrate pending a November 9 hearing. Lawyers for Martin declined to comment. Assistant Attorney General for National Security John A. Eisenberg said the letters represented a "calculated attempt to terrorise public servants... Intimidation like this has no place in a Nation governed by the rule of law." The FBI said mailings in early October were addressed to state election officials in all 50 states. It also believes Martin had sent threatening letters in 2024 to election and postal officials. The threatening letters in October bore an outdated return address of the Democratic Socialists of America (DSA) in New York, the FBI said. Read: FBI launches investigation into suspicious packages sent to election offices It added that Martin had also made contact with the DSA in August and obtained the email addresses of DSA members, after which they were added to a mailing list that sent them threatening messages, warning they could be arrested if they voted. The FBI also linked Martin to a threatening letter in 2024 that "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." The FBI tied the letters to Martin through surveillance video from postal facilities and a Walmart, where a phone believed to have been used in the threats had been purchased. The government said Martin had also written a letter to FBI Director Kash Patel that was determined to have Martin's fingerprints. The letter had a message written in ultraviolet-reactive ink reading "FBI SAVE THE USA" that was also on other threatening letters.