BOSTON >> A Massachusetts man who sent threatening letters with white powder to President Donald Trump’s sons, Antonio Sabato Jr., Sen. Debbie Stabenow and a law professor was sentenced Friday in federal court to five years of probation.

The judge declined to send Daniel Frisiello to prison, as prosecutors had sought, because of concerns the 25-year-old man from Beverly, who is developmentally disabled, would not respond well to incarceration. But he stressed the sentence wasn’t “lenient.”

“Do not underestimate how serious I am treating your crimes,” Judge Nathaniel Gorton said to Frisiello as the dozens of his family members, friends and supporters who packed the court proceeding hugged, cried and sighed in relief.

Frisiello was also ordered to serve his first year of probation in home confinement, and has been banned for the full five years from accessing the internet or sending mail without prior approval. Frisiello also won’t be allowed to have a computer, tablet or other device with access to the internet.

Frisiello, who pleaded guilty in October to sending the threatening letters, thanked Groton for not imprisoning him. The past year, he said, has been “hell” for his family.

Frisiello’s family, in a statement after the court appearance, said he “deeply regrets the fear and harm he caused and will work very hard to be a better person and citizen.”

Assistant U.S. Attorney Scott Garland, who had sought a three-year prison sentence, argued that Frisiello had carefully considered the letter writing campaign, which included 13 letters over three years. He researched the best addresses and took steps to avoid detection, like dropping them off at different mailboxes, Garland said.

“This was not an impulsive thing,” he said. “At every step, there was a chance for deliberation.”

Imposing only probation, Garland said, was akin to sending Frisiello back to the life he had before his arrest, which was largely spent at home on the internet.

Frisiello lawyer’s William Fick argued that prison would be physically and mentally harmful to his client, who he said has significant developmental issues from brain damage at birth, autism and anxiety disorder.

Fick also argued probation is appropriately severe for a person with Frisiello’s condition because it takes away what few opportunities he has to interact with society, such as going to work or spending time with family and friends outside the house.

Acknowledging the nearly 90 letters of support written to the judge on Frisiello’s behalf, Fick said it was “tragic” no one in his client’s extensive support network intervened before his seemingly harmless obsession with writing letters to celebrities and other notable people took a dark turn.

“He clearly felt like he wasn’t being heard, so he became threatening,” Fick said.

Prosecutors say Frisiello sent a letter to Donald Trump Jr. that was opened in February by his now-estranged wife, Vanessa, at their New York City home. She called 911 and was briefly hospitalized after she reported she was coughing and felt nauseous.

He also sent a white powder letter to Eric Trump during the 2016 presidential campaign that said his father must drop out of the race or the next letter wouldn’t be fake.

The substance in all of the letters turned out not to be hazardous.

Other letter recipients included Stabenow, the Democratic U.S. senator from Michigan; Michele Dauber, a Stanford University law professor who promoted an effort to recall California judge Aaron Persky; and Sabato, a former underwear model and soap opera actor who is running for Congress in California as a Republican and spoke at the 2016 Republican National Convention.

Hoaxes involving white powder have been common since anonymous letters laced with anthrax spores were sent to media companies and congressional offices days after the terrorist attacks of Sept. 11, 2001, killing five people and infecting 17 others.