U.S. Sen. Lamar Alexander has replaced his chief of staff after learning his top aide’s home was being searched as part of a child pornography investigation.

Alexander said in a statement Wednesday that it’ll be up to the courts to judge Ryan Loskarn, but “under these circumstances, he cannot continue to fulfill his duties as chief of staff.”

Alexander named his legislative director, David Cleary, as his new chief of staff.

Alexander said he was “stunned, surprised and disappointed” by the allegations against Loskarn.

U.S. Justice Department spokesman Peter Carr said in a statement that Loskarn was arrested based on probable cause for possession and distribution of child pornography charges.

Video taken at the scene by WJLA-TV shows Loskarn being led from his southeast D.C. home by U.S. Postal Inspector police who put him into a black SUV. Loskarn appears to be in handcuffs, although a coat is draped over his arms.

The U.S. Postal Inspection Service often handles child pornography investigations.

Loskarn, who is well-known on the Hill, remained in custody Wednesday evening pending a federal court hearing in Washington, D.C.

Carr said more information would be released as it is provided to the court or unsealed.

Earlier in the day, Alexander placed Loskarn on immediate administrative leave without pay and announced that his office was fully cooperating with the investigation.

Alexander is a former Tennessee governor and has also served as the U.S. Secretary of Education. He was first elected to the Senate in 2002, and is seeking a third term in the Senate in next year’s congressional elections. While he is facing a challenge in the Republican primary, Alexander is thought to be in position to be re-elected.

According to Loskarn’s biography on his LinkedIn account and in previous communications for Alexander’s office, Loskarn graduated from Tulane University in 2000 and went to work for retired Republican U.S. Rep. Wally Herger of California as a legal assistant. He later was the communications director for U.S. Rep. Marsha Blackburn, a Tennessee Republican, and eventually became staff director for the Senate Republican Conference. He has also worked for former Sen. Jon Kyl or Arizona. Loskarn has served as Alexander’s chief of staff for two years.

U.S. Rep. Blackburn released a statement on Tuesday saying, “I am shocked, saddened, and stunned by these allegations.”