Well, they could have easily gotten the so called CIA "letter opener" through security. It's available from cheap knife sellers at flea markets across the country and from a lot of online sources:
Here's a description from one website that sells them. They sell pretty well at flea markets in urban areas to students who attend high schools that use metal detectors looking for guns and knives.
With the help of Blackie Collins, Shomer-Tec has updated the classic, but decades-old, C.I.A. letter opener for the new millennium. This updated version is made from GV6H, the high-tech composite from Switzerland made with 60% glass fibers.
This completely non-metallic letter opener provides superior plunging power as well as a hard edge. The scalloped serrated edge on one side gives additional opening power on fiberous materials. The built-in clip eliminates the need for a sheath since it can clip directly to a belt,pants, sock, etc. The contoured handle is comfortable to hold and has a thumb depression for a secure grip. There is a hole in the handle for attachment of a lanyard. The CIA letter opener is completely non-metallic, non-magnetic, and non-absorbent, making this a perfect item for EOD personnel. Total length 7.5" non-reflective black. Price $10.00