Not true.
Signed in Bill Clinton's tenure? It basically says 'any US citizen violating a US law is guilty of breaking that law, regardless of their location at the time of the event. 'It goes on to say that any 'US citizen breaking a law of a [specific] foreign countries is then a felon in the US.'
http://www.uniset.ca/other/cs6/253F3d234.html
In 1998, Thomas Bean, an FFL, was in Laredo participating in a gun show. One evening he crossed the border into Mexico for dinner. A box of ammo was found in his vehicle by Mexican customs officers. At the time importing ammunition into Mexico was considered a felony. Bean was charged and convicted of the felony of unlawfully importing ammunition. As a convicted felon, Bean lost all rights to possess firearms when he returned to the US.
<quote>
( If I'm in Mexico and kill an American, I broke Mexican law, not US law, so deciding they are undesirable people, then inviting them to the US to arrest them for breaking US law when they never set foot there before is insane). </quote>