Prosecutors are seeking three years in prison for a Massachusetts man who admitted to sending threatening letters filled with white powder to President Donald Trump's sons and others.

Daniel Frisiello is set to be sentenced Friday in Boston federal court. He pleaded guilty in October.

The letter Frisiello sent to Donald Trump Jr. was opened last year by his now-ex-wife, Vanessa. She was briefly hospitalized as a precaution after she reported feeling ill. The substance turned out to be nonhazardous.

Other recipients of Frisiello's letters included Democratic U.S. Sen. Debbie Stabenow of Michigan.

Frisiello's lawyer is seeking five years of probation, including one year of home confinement. His lawyer says the 25-year-old has developmental delays, is autistic and would be susceptible to "exploitation, violence and isolation" in prison.