The congressional hearing on an internal investigation into Operation Fast and Furious scheduled for Tuesday has been postponed until next week.

The U.S. House Oversight Committee had planned to question Justice Department Inspector General Michael Horowitz on Tuesday, but the hearing will take place Sept. 19, the committee announced.

The committee didn’t explain its decision, but in a letter to the committee sent Sept. 5, Horowitz warned he may need more time to finalize the report. He said the department needs to delete from the report secret information derived from sources such as grand jury hearings and wiretaps.

Bureau of Alcohol, Tobacco, Firearms and Explosives special agents launched Operation Fast and Furious in September 2009, attempting to bring down a cross-border gun-trafficking network. ATF agents allowed suspects to leave the country with hundreds of weapons, and two of the suspect guns were found at the scene, west of Rio Rico, of the Dec. 14, 2010, killing of U.S. Border Patrol agent Brian Terry.