Daniel Frisiello, of Beverly, Massachusetts, was arrested by the FBI Thursday.
As Trump Jr.'s wife, Vanessa, opened the envelope February 12, white powder spilled out, and she was taken to a New York City hospital. This prompted a brief law enforcement response on the East Side.
Frisiello was charged with sending at least five letters containing "suspicious white powder" with threatening messages to elected officials, officials said.
At least five locations across the country have received a similar envelope with a Boston postmark, suspicious white powder and a written message.
The letter addressed to Donald Trump Jr. was sent to his mother-in-law's apartment on East 54th Street in Manhattan and postmarked in Boston on February 7.
It contained a typewritten note reading, "You are an awful, awful person. I am surprised that your father lets you speak on TV. You make the family idiot, Eric, look smart. This is the reason why people hate you, so you are getting what you deserve. So shut the F--- UP!"
PHOTOS: Scene of Donald Trump's apartment in NYC
The other recipients include a U.S. Attorney in Los Angeles, a law professor at Stanford University, Sen. Debbie Stabenow of Michigan and actor Antonio Sabato Jr, who is running for Senate in California.
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