Explosive evidence that will not wash away

From The New Scientist, 11:52 19 February 04
"Bombers and bomb makers could soon be exposed by testing their hair for traces of explosives.

Jimmie Oxley, a chemist at the University of Rhode Island, Kingston, has extracted nanograms of the common explosives TNT, RDX and PETN from the hair of workers who handle these chemicals daily when training airport sniffer dogs. Even after several washes and brushing, the explosives still showed up in chromatography tests on a solvent-soaked comb that was run through the hair."
This we knew, right? A little surprised it lasts that long; however, this is for employees who handle the chemicals daily. What about if the bomb builder is not the bomb deliverer? I think this would be common. We'll have to see the paper she presents at the SPIE Defense & Security Symposium.