A former computer systems administrator for Senator Maggie Hassan’s office pleaded guilty to computer fraud and four other counts Friday, according to the US District Court in Washington, D.C.
Jackson Alexander Cosko, 27, pleaded guilty to superseding information, including two counts of making public restricted documents, one count of computer fraud, one count of witness tampering, and one count of obstruction of justice, court documents show .
Cosko allegedly obtained keys from another Senate staffer. He entered the office alone at night to install “keylogger” devices, which record keystrokes, on six staff computers, according to the document.
Officials say Cosko was caught by a staffer on one occasion and fled, then sent the staffer an e-mail stating, “If you tell anyone I will leak it all.”
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Using information gathered by these devices, Cosko allegedly copied dozens of gigabytes of data, including credit card information and social security numbers belonging to Senate employees, personal information from hundreds of other people, and tens of thousands of e-mails, according to officials.
Hassan is a Democrat from New Hampshire.
Cosko is also accused of “maliciously” publishing the personal home addresses and phone numbers of Senators Lindsay Graham, Orrin Hatch, and Mike Lee while watching the Judge Brett M. Kavanaugh hearing, according to the document.
Cosko also allegedly published the personal home addresses and telephone numbers of Senator Rand Paul and Senate majority leader Mitch McConnell.
Under federal sentencing guidelines, Cosko could face 30 to 57 months in prison, according to the document.
Cynthia Fernandez can be reached at cynthia.fernandez@globe.com.