Daniel Frisiello, 24, was arrested after what prosecutors called "a textbook federal investigation" that traced the unsigned letters to him after he also ordered a "glitter bomb" for one of the recipients, using his own name.
The powder in the letters was not dangerous. The FBI said Frisiello — who was suspended from his job at Catholic Charities' Peabody Child Care Center — is cooperating. He is charged with mailing threat to injure and false information and hoaxes.
Each letter had a different complaint and referenced recent news events — from the sexual abuse conviction of former gymnastics doctor Larry Nassar to the sexual assault case of former Stanford student Brock Turner.
The letter sent to California U.S. Attorney Nicole Hanna accused her of "murdering" former "Glee" star Mark Salling, who killed himself after being prosecuted for child pornography.
"I hope you end up in the same place as Salling," it said.
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Sen. Debbie Stabenow, D-Mich., was targeted because she defended Randall Margraves, a father who charged at Nassar during his sentencing for molesting former patients.
"If you condone Margraves reaction to his daughter's testimony on Dr. Nassar, you are no better than he is," read the letter, which went on to use vulgar language.
The note to Sabato, a supporter of President Donald Trump who is running for a congressional seat, railed at him for his political views.
They discovered that Dauber, the law professor, had also received what's known as a "glitter bomb" that contained the same message as the letter with the white powder. The glitter letter indicated it came from the website www.shipyourenemiesglitter.com, and the company owner confirmed Frisiello had ordered it, according to court documents.
The owner said Frisiello attempted to send another 10 glitter bombs, including some to members of President Trump's family but he declined to process the order because the messages appeared threatening or inappropriate.
Frisiello's Facebook page contained posts about the recipients of the letters, authorities said. The account cited in court papers was still active on Thursday; in the most recent post, Frisiello criticized Prince Harry's fiancee, Meghan Markle, for endorsing the #timesup movement.