This item has been updated.

The chief of staff to Sen. Lamar Alexander (R-Tenn.) was arrested Wednesday on charges of possessing and distributing child pornography -- and swiftly fired by the senator.

Jesse Ryan Loskarn, 35, of the District, was arrested at his home Wednesday afternoon by the U.S. Postal Inspection Service and is expected to appear in federal court in Washington on Thursday to face charges, the Justice Department said.

Word of the investigation was first revealed in a statement issued Wednesday morning by Alexander, who said he was "stunned, surprised and disappointed" by the news and would be placing Loskarn on unpaid administrative leave. The news spread quickly across Capitol Hill among Loskarn's colleagues and friends in the close-knit worlds of congressional staffers and Capitol Hill reporters with whom he worked with for years.

Alexander later announced that he had “removed” Loskarn from his staff and replaced him with another longtime aide, David Cleary.

Like many longtime congressional staffers, Loskarn climbed the ranks on the House side of Capitol Hill before moving to the Senate. He began as an aide to former Rep. Wally Herger (R-Calif.), moved to the press staff of the House Rules Committee and spent four years as a spokesman for Rep. Marsha Blackburn (R-Tenn.)

Considered by colleagues and the Capitol Hill newspaper Roll Call to be a deft communications staffer with access to top aides and senators, he became a spokesman for the Senate Republican Conference – the messaging shop for Republican senators – in 2007. He became staff director in 2009 when Alexander assumed control of the office and became the chief of staff of Alexander’s personal office when the senator stepped down from his leadership role in hopes of helping to broker bipartisan agreement.

Sean Sullivan contributed to this report.