Authorities say a worker who killed himself inside an Alabama federal courthouse went through an employee entrance to avoid a security check that could have caught the gun.

The U.S. Marshals Service says the worker used an access card to enter the Hugo L. Black U.S. Courthouse in Birmingham on Thursday morning. The card system is in place while renovation work is being done on the main entrance.

He didn't walk through metal detectors that are staffed by security officers to prevent weapons from entering the building. Officials say those procedures are now under review.

Police Sgt. Johnny Williams says the worker shot himself once in the head in a first-floor clerk's office. No one else was threatened.

• Hugo L. Black U.S. Courthouse, Birmingham, AL