NASHVILLE (AP) - U.S. Sen. Lamar Alexander has replaced his chief of staff after learning the staffer'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.

Several messages left for Loskarn were not immediately returned.

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

On Wednesday afternoon, Loskarn remained in custody pending a court hearing expected to be scheduled for Thursday in federal court in Washington, D.C.

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

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. He said his office is fully cooperating with the investigation.

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.

Loskarn had se rved as Alexander's chief of staff for two years.

Blackburn released a statement Wednesday saying, "I am shocked, saddened, and stunned by these allegations."