[roywiggins]

The US doesn't care much where you physically are when you commit a crime against the US. For instance, if you conspire to traffic drugs into the US, the US can come after you. It doesn't matter if you're physically in the US or not when you do it.

If an estranged noncitizen parent living abroad conspires to kidnap his children from their custodial parent inside the US, he can be tried for kidnapping by the US. Even if his part of the conspiracy never takes place inside the US. The alternative- just letting him off, due to where he happened to physically be at the time- would be fairly absurd. The jurisdiction he's physically in probably doesn't care, and even if they do, most of the witnesses and all of the victims are physically in the US.

The US can't kidnap him but asking the jurisdiction he is in to extradite him is totally normal. This is what extradition agreements are for, in part.