[OneTimeLurker]

Left behind by a trade doing some work, no doubt. I doubt terrorists accidentally leave behind their weapons.

[LenS]

Or it could simply have been some lady had forgotten that she had it on her when she reached the airport. The quickest and easiest thing to do is to go in the bathroom and throw it away. Trying to give it up to security would just make you miss your flight as they interrogated you.