New Orleans ? The top federal prosecutor for New Orleans has removed himself from the case of four conservative activists arrested last week while trying to capture hidden camera footage in a senator’s office, the Department of Justice said Monday.

A Justice Department news release said Jim Letten, U.S. attorney for the Eastern District of Louisiana, recused himself from the case a day after the Jan. 25 arrests in Democrat Sen. Mary Landrieu’s office in New Orleans. Letten’s top lieutenant, assistant U.S. Attorney Jan Mann, has taken over.

The news release didn’t say why Letten removed himself, and his spokeswoman Anna Christman said she couldn’t comment.

One of the suspects is the son of Letten’s Shreveport-based counterpart.

Another man who was arrested, daredevil videographer James O’Keefe, has said the group wanted to investigate complaints that constituents calling Landrieu’s office couldn’t get through to criticize her support of a health care reform bill. Landrieu’s office has said O’Keefe’s explanation is feeble, and the case should be thoroughly investigated.

Authorities said O’Keefe used his cell phone to try to capture video of two other men who posed as telephone repairmen and asked to see the phones at Landrieu’s office. The fourth is accused of waiting outside in a car with a listening device that could pick up transmissions.

O’Keefe is known nationally for hidden-camera videos targeting the community-organizing group ACORN.