MOSCOW — The Russian spam kingpin had long been in the cross hairs of the F.B.I., and agents finally got their shot when the man scheduled a vacation in Spain. At the agency’s request, Spanish security officers in April arrested the man, Pyotr Y. Levashov, who is accused of stuffing untold millions of inboxes with ads for pornography, pills and penny stocks.

But then the Russian authorities sprang a trap of their own, filing an extradition request with the Spanish authorities for a crime they said Mr. Levashov had committed in Russia years ago. Currently, he is languishing in a Spanish jail, but soon the authorities will have to decide which extradition request to honor: the United States’ or Russia’s.

This was by no means the first time that Russia had filed a competing extradition request. Far-fetched as it may seem, the Russians’ tactic has in several instances prevented Russians suspected of being computer criminals from being deported to the United States while detained in Europe.

The tactic has raised suspicions that the Russian authorities are more interested in derailing American investigations and possibly protecting criminals they find useful than they are in fighting cybercrime.