Authorities arrested a Massachusetts man Thursday on suspicion of sending threatening letters to five high-profile Americans, each containing a suspicious white powder, according to officials with the U.S. Secret Service.

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Officials said Daniel Frisiello, 24, of Beverly, is accused of mailing letters addressed to the president’s son, Donald Trump Jr.; interim U.S. attorney for the Central District of California Nicola Hanna; Stanford University law professor Michele Dauber; U.S. Sen. Deborah Stabenow, D-Michigan; and Antonio Sabato Jr., a candidate for a congressional seat in California.

“Beyond terrifying the victims, these incidents caused law enforcement agencies around the country to spend time and money deploying emergency response units,” U.S. Attorney for the District of Massachusetts Andrew Lelling said in a news release. “Thankfully, the white powder in these letters was inert and no one was harmed.”

Frisiello's attorney, Scott Gleason, told The Associated Press that his client planned to plead not guilty Thursday. He described Frisiello as "an overwhelmed young man."

The letter addressed to Trump Jr. contained corn starch, law enforcement sources told The New York Times last month, although authorities weren’t able to confirm that until after Trump Jr.’s wife, Vanessa, and his mother-in-law, Bonnie Haydon, were hospitalized out of precaution.

Police: Donald Trump Jr.'s Wife Receives Letter With White Powder And Taken To Hospital

Vanessa Trump was the one to open the letter when it arrived at Haydon’s Manhattan apartment. It contained a note for Trump Jr. that said, “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 (expletive) UP!”

>> Related: Letter sent to Donald Trump Jr.'s wife contained corn starch, police say

“While we determined that the mailings did not contain toxins or poison, each of these incidents required a significant law enforcement response, a field screening of the letter’s contents, and a methodical analysis by FBI weapons of mass destruction and laboratory experts,” said Harold Shaw, the special agent in charge of the FBI’s Boston field division.

“All this comes at a cost to taxpayers’ money and diverted first responders and other limited resources away from actual emergencies.”

Hanna got another of the letters from Frisiello, investigators said. Like the letter to Donald Trump Jr., Hanna’s envelope was postmarked in Boston on Feb. 7 and contained a suspicious white powder.

Hanna’s office had been pursuing a child pornography case against Mark Salling, best known for his role as Noah “Puck” Puckerman on “Glee,” before the actor committed suicide in January.

“That’s for murdering Mark Salling!” a letter sent with the powder said, according to the U.S. Secret Service. “I hope you end up (in) the same place as Salling.”

Dauber was also sent a “glitter bomb” -- a letter containing glitter that is meant to spill onto the unwitting recipient when it’s opened -- which investigators said they traced to Frisiello.

Frisiello faces five counts each of mailing a threat to injure the person of another and false information and hoaxes.