I would do this for someone I had known for 20 years and trust with my life. Nobody else.
It may be that the duty is the least of the issues and it may be that the guy is completely honest and just wants a favor. If the former, you may cause yourself immeasurable harm and if the latter, you are playing Fedex when there are any number of reliable services which transport valuables bonded properly and for the fees those services command. The friend's jeweler will know those services if this is legit.