The Saudi was probably cleared as a suspect and flown home for his own safety due to diplomatic issues . . . I doubt the phrase "national security" was ever used. Immediately after 9/11 when all flights were grounded and it was discovered that the terrorists were Saudi nationals, dozens of members of the Saud royal family were permitted to fly home. Very few details were disclosed there either. The U.S. has maintained strong diplomatic relations with the House of Saud for decades, and if the guy was cleared as a suspect this is not too unusual for them. While it may be possible the bomber was Saudi, it wasn't THAT Saudi.