BAY CITY (AP) — Federal prosecutors charged a Michigan man with threatening the life of an attorney for the whistleblower who spurred the impeachment inquiry of President Donald Trump.

Brittan Atkinson, 52, of Beaverton, was ordered temporarily detained during an initial court appearance Thursday in Bay City and a not guilty plea was entered on his behalf. A detention hearing was scheduled for Monday, The Detroit News reported.

Stevens Jacobs, Atkinson’s court-appointed attorney, did not immediately return a call from The Associated Press seeking comment.

According to an unsealed indictment, Atkinson said in an email to a lawyer to the whistleblower, “All traitors must die miserable deaths,” and “those that represent traitors must meet the same fate.”

The lawyer isn’t identified, but attorney Mark Zaid confirmed in emails to the newspaper and Politico that he received the email that authorities say was sent by Atkinson. The email was sent a day after Trump criticized Zaid during a November rally in Louisiana, The News reported.

“My job was to ensure the rule of law was followed in how whistleblowers are treated,” Zaid told the newspaper in an email. “It’s not appropriate for anyone to threaten another individual’s life, regardless of political views.”

Trump has harshly criticized the whistleblower, saying, “That person’s a spy in my opinion,” and he has falsely argued that the whistleblower’s claims were inaccurate. And while Trump acknowledged whistleblowers should be protected, he added the caveat “if the whistleblower is legitimate.”

U.S. whistleblower laws exist to protect the identity and careers of people who bring forward accusations of wrongdoing by government officials. Lawmakers in both parties have historically backed those protections.