WASHINGTON – A former staff member who worked in an office of a United States Senator pled guilty today to federal charges stemming from his theft of Senate information and the illegal posting of restricted personal information of five U.S. Senators on the Wikipedia website, as well as related conduct.

The announcement was made by Alessio D. Evangelista, the Acting U.S. Attorney in this case, and Matthew R. Verderosa, Chief of the U.S. Capitol Police.

Jackson A. Cosko, 27, of Washington, D.C., pled guilty to five federal offenses: two counts of making public restricted personal information; one count of computer fraud; one count of witness tampering, and one count of obstruction of justice. Under federal sentencing guidelines, which are to be calculated at a later date, Cosko could face a prison term within the range of either 30 to 37 months or 46 to 57 months. The plea agreement requires Cosko to forfeit computers, cellphones and other equipment used in the crimes. The Honorable Senior Judge Thomas F. Hogan scheduled sentencing for June 13, 2019.

According to the government’s evidence, the U.S. Capitol Police began an investigation on Sept. 27, 2018, after it was determined that the Wikipedia pages of three U.S. Senators had been edited to include restricted personal information without their knowledge or permission. This information included home addresses and personal telephone numbers. These edits took place roughly contemporaneously with public – and highly publicized – Senate proceedings related to a nomination for the U.S. Supreme Court. Then, on Oct. 1, 2018, similar information was posted on the Wikipedia pages of two additional Senators.

“Doxxing” is the act of gathering, by licit and illicit means, and posting on the Internet personal identifying information (“PII”) and other sensitive information about an individual.

In a statement of offense submitted as part of today’s plea, Cosko admitted that he had been angry about his termination in May 2018 from his employment as a computer systems administrator in the office of another U.S. Senator (described in court documents as Senator #1). As a result, beginning no later than July 2018 and continuing until October 2018, he engaged in an extensive computer fraud and data theft scheme. He admitted that he carried out the scheme by breaking into Senator # 1’s office on at least four occasions and accessing Senate-owned computers for the express purpose of stealing proprietary electronic information, including the personal contact information for numerous other Senators. He then published the contact information for five U.S. Senators (identified as Senators #2, 3, 4, 5, and 6) using Wikipedia and Twitter, with the intent to threaten and intimidate these five Senators and their families.

On the night of Oct. 2, 2018, according to the evidence, a witness saw Cosko at a computer in Senator # 1’s office. The witness confronted Cosko, who left the office. Later that evening, according to the statement of offense, Cosko sent a threatening e-mail to the witness, titling it, “I own EVERYTHING” and warning that, “If you tell anyone I will leak it all.” Additionally, that evening Cosko attempted to delete electronic evidence from items including a laptop computer that he used to obtain and download the stolen data.

An investigation led to Cosko’s arrest the following day by the U.S. Capitol Police.

This case was investigated by the U.S. Capitol Police. It is being prosecuted by Assistant U.S. Attorneys Demian S. Ahn, Tejpal S. Chawla, and Youli Lee. Assistance was provided by Paralegal Specialists Diane Brashears and Matthew Ruggierio and Victim/Witness Advocate Yvonne Bryant, all of the U.S. Attorney’s Office for the District of Columbia.