But 9/11 wasn't the original catalyst. On April 19, 1995, Timothy McVeigh detonated a truck bomb in front of the Alfred P. Murrah Federal Building in Oklahoma City, killing 168 people. President Bill Clinton responded by directing the Justice Department to produce a report on the vulnerability of federal facilities to acts of violence. The so-called "Marshals Report" recommendations led to new construction standards and a paradigm shift in building design.
Above, the north side of the Murrah Building after the truck-bomb explosion.