WASHINGTON (CNN) -- Senate Democrats announced Tuesday that former U.S. Capitol Police Chief Terry Gainer will serve as the Senate Sergeant at Arms, the top law enforcement position in the Senate.

In March, Gainer stepped down after nearly four years as police chief when questions were raised about the propriety of his son-in-law being hired on the force.

Gainer, popular with rank and file officers, became known nationally after 9-11 and the anthrax attacks on the Capitol that followed. But he had a rocky relationship with key Republican appropriators in the House, many of whom complained he sought the limelight.

He replaces former Secret Service agent William Pickle, a confidant of Senate Majority Leader Bill Frist, who has held the job since 2003.

In his new role, Gainer will serve on the U.S. Capitol Police Board, a three member panel that oversees the U.S. Capitol Police.