A U.S. judge on Wednesday sentenced a former Democratic Senate staff member to four years in prison for a burglary and hacking campaign that culminated in the single largest known theft of electronic data from the Senate and the posting of private information about Republican senators on the Internet.

Jackson A. Cosko, 27, of the District, pleaded guilty in April to “doxing” the senators after being fired by one senator and growing angry at others while watching the Sept. 27 Senate hearing that addressed sexual assault allegations against then-Supreme Court nominee Brett M. Kavanaugh.

Cosko subsequently doxed five senators by anonymously editing their Wikipedia pages to add phone numbers and home addresses, he admitted to the court. The information was quickly removed after the alterations were discovered, and aides contacted authorities.

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In addition to two counts of disclosing restricted personal information and one count each of computer fraud, Cosko confessed to one count each of witness tampering and obstruction of justice by threatening a staffer who caught him on a computer in the office of Sen. Maggie Hassan (D-N.H.), where he was a computer administrator before he was fired in May 2018.

Judge Thomas F. Hogan of the U.S. District Court for the District of Columbia said Cosko intended to hurt people with whom he disagreed, committing a “vicious offense” in an increasingly “intemperate and uncivil” world in which, the judge noted, a gunman in 2017 opened fire on Republican lawmakers at a baseball practice and Democrats faced similar threats, including from a mail bomber in Florida.

“People should realize, especially young people, you simply cannot do this without facing serious consequences,” Hogan said.

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Also Wednesday, prosecutors charged another Hassan staffer they allege had been persuaded by Cosko to try to “wipe down” Senate computers he hacked.

Samantha Deforest Davis was charged with two misdemeanors — one federal count of aiding and abetting computer fraud and one District count of attempted evidence tampering — in a criminal information, a type of charging document that is used when a defendant waives indictment and that can signal an intent to plead guilty.

Davis’s assistant federal defender, Shelli Peterson, declined to comment.

In plea papers, Cosko acknowledged that the senators he doxed were GOP Senate Judiciary Committee members Lindsey O. Graham (S.C.); and Mike Lee and Orrin G. Hatch, both of Utah; as well as and Rand Paul and Senate Majority Leader Mitch McConnell, both Republicans from Kentucky.

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“The defendant deliberately and maliciously committed serious crimes directed at United States senators and the Senate,” imposing significant harm on individuals senators, their families, staff and the Senate, Assistant U.S. Attorney Demian S. Ahn said in requesting a 57-month prison sentence.

Ahn urged the judge to impose a penalty to deter others, saying that Cosko’s “crimes call out for a significant sentence,” having been committed in an environment of a rise in politically motivated “criminal harassment and threats.”

Cosko’s attorneys argued for a two-year term, saying he cooperated fully with investigators, alerting police to a co-defendant, and also to keystroke-logging equipment he had placed on Senate machines and to key evidence missed in a police search. Supporters wrote to the judge saying they were shocked by Cosko’s actions, which they attributed to a spiral of untreated mental-health problems and massive consumption of psychedelic drugs, cocaine and alcohol last year.

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“I accept full and complete responsibility for my actions,” Cosko said in court, backed by his parents, siblings and cousins. He apologized for the harm he caused to the Senate, staffers, constituents and the U.S. Capitol Police, and the disappointment and humiliation he inflicted on his family.

Cosko has served about four months in jail and five months in treatment since his arrest. “I believe it saved my life, and moving forward I intend to take full advantage of that to live a purposeful life,” he said.

Hogan agreed to recommend that Cosko serve his sentence at the federal low-security prison at Lompoc, Calif., near his parents, and participate in a U.S. Bureau of Prisons residential drug rehabilitation program. Hogan noted that a federal presentencing investigation found that Cosko had been consuming various drugs in what should have been fatal quantities. “I find it almost incredible or unbelievable that you could even operate anything,” Hogan said.

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Cosko’s attorney Brian W. Stolarz said, “No one should be judged by their worst act but how they emerge from it.”

Cosko was arrested Oct. 3 by Capitol Police, who said he had been caught sneaking into Hassan’s offices after 10 p.m. the night before and using an aide’s computer and log-in, according to court filings.

Another aide recognized Cosko, ordered him to leave and called police, Cosko acknowledged in plea papers. Minutes later, that aide received a threatening email with the subject line “I own Everything” and a text stating, “If you tell anyone I will leak it all. Emails signal conversations gmails. Senators children’s health information and socials,” according to plea papers.

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Cosko had burglarized the office several times, copying network drives and identifying sensitive information he might use later, he admitted in court filings.

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The five federal felony counts to which Cosko pleaded guilty carried maximum penalties of up to 20 years in prison.