If the soviets abandoned the search for their sub, is it really stealing if you salvaged it from international waters? If they wanted to keep claim they should have stuck around looking for it.
Stealing isn't really a concept between states, I believe, but this would qualify. "Giving up the search" doesn't equal "abandoning your property rights". If you find something, pocket it, and don't take the appropriate steps to try to return it to it's rightful owner, you're guilty of theft/stealing/larceny by finding.
Original headline was too long to submit. Full headline:
"During the Cold War, the C.I.A. Secretly Plucked a Soviet Submarine From the Ocean Floor Using a Giant Claw"