I respectfully disagree with EPGWS-- it could be done in a few keystrokes on the FMS if he had inside knowledge. He wouldn't need knowledge of the other FMS functions. He might have been able to learn the keystrokes from Microsoft Flight Simulator.
He could also do it another way-- just bring a handheld GPS with him, programmed with coordinates for the target.
I don't think it's healthy to underestimate the cunning of these otherwise goofy suspects.
Microsoft Flight Simulator review excerpt:
For those wishing to engage in the experience of flight there are GPS navigation systems aplenty, dozens of cockpits switches and an air traffic control system which is as lifelike as it bewildering to understand.
http://www.amazon.co.uk/exec/obidos/ASIN/B00009WAPR/ref=br_lf_vg_h__0/026-4262603-2799608
What is an FMS? Does that have to do with a GPS? I really do not understand very much.
I also remember they had trouble maintaining altitude, though I don't know what reason was given for that....
Apparently he didn't however for he couldn't even shut off the auto pilot disconnect horn which is a simple push of a button on the control yoke.