Ronald Derisi was arrested for allegedly threatening to assault and murder two U.S. senators over their support for Brett Kavanaugh's nomination to the Supreme Court. (File photo).

A New York man was arrested Friday morning for allegedly threatening to murder and assault two U.S. senators because of their support for the successful nomination of Brett Kavanaugh to the Supreme Court, federal authorties said.

The man, 74-year-old Ronald DeRisi of Smithtown, Long Island, phoned in his expletive-laden threats to the offices in the home states of the senators, according to a federal complaint lodged against him. The complaint did not identify the senators.

DeRisi previously pleaded guilty to a state charge of aggravated harassement, which was related to his repeatedly phoning a victim's home and office more than 15 times in 2015 to leave threatening messages.

The new complaint says that DeRisi, starting on Sept. 27, left more than 10 "threatening voice-messages" at the offices of the two senators regarding Kavanaugh's then-pending nomination.

The threats apparently were made to discourage the senators from supporting Kavanaugh "and/or as retaliation for having voted to confirm Judge Kavanaugh" later, according to a statement by the United States Attorney's Office, which is prosecuting the case.

The complaint said DeRisi used a pre-paid cellphone to make the threatening calls from or around his home.

DeRisi's lawyer, Peter Brill, told CNBC that his client was diagnosed after his 2015 arrest with "cerebral atrophy which has led to progressive dementia."

"He's not a violent person, although his disease has led to an increased lack of impulse control," Brill said. "We know this story was scary to the people he called, but he's not a violent person and I'm just going to continue to hope that he gets th help that he needs."

The arrest comes two days after the husband of Sen. Susan Collins, R-Maine, said he received a threatening letter that referred to Collins' support for Kanvanaugh, and which claimed to be tainted with the deadly toxin ricin.

Tests showed there was no danger from the letter, but Collins' husband, Thomas Daffron, and the couple's Labrador retriever, Pepper, were quarantined before the test results. The person responsible for the letter to Daffron has not been apprehended.

In one message cited in the complaint unsealed in New York, DeRisi on Sept. 27 left a voice message that said he had a "present" for the first senator, saying, "It's a nine millimeter. Side of your ... skull.

"Yeah, Kavanaugh — I don't think so," DeRisi said, according to the complaint. On the same day, the complaint said, DeRisi left another message for the same senator, saying "If f----- Kavanaugh get's in, he's dead f------ meat!"

In an Oct. 6 call to the second senator, which was the same day Kavanaugh was confirmed, DeRisi said, "You better pray this guy don't get in."

"I'm gonna get you," DeRisi said in a follow-up message to the same senator, the complaint charges.

DeRisi was identified through phone records, voice exemplars and the debit card he used to buy the pre-paid cell phone, according to authorities.

After his arrest, United States Capitol Police, who led the investigation, executed a search warrant and seized the cell phone used to leave the threatening messages, prosecutors said.

"We and all those dedicated to the rule of law will not tolerate the use violence and threats of violence in attempts to prevail in political disputes," said Richard Donoghue, the U.S. Attorney for New York's Eastern District.