The official account of the 1995 Oklahoma City bombing is being challenged again, and the pressure falls on the FBI and the Justice Department to explain gaps in their own records.

• The government has always said one man built and set off the truck bomb that killed 168 people, acting alone.
• Security camera footage from around the federal building was collected by the FBI, but key parts of the tapes came back blank.
• Federal judges across the street and the local fire department got a general warning that morning; the workers inside the building and the daycare center did not.
• Witnesses reported seeing a bomb squad checking the building before the blast, and more than 50 people said they saw a second man with the bomber in the weeks beforehand.
• The government offered a $2 million reward for that second man at the time, and now says he never existed.

Outlook: Expect renewed calls to release the original tapes and files, with the missing footage the hardest thing for the government to explain.