Legal grounds? Does it matter?
Suddenly, pirates, out of fucking nowhere.
EDIT:
Seriously, I wouldn't be surprised if some "random" thing happened to Snowden if he tried to go by a boat. Just like Assange became an sex offender out of the blue the moment he seriously pissed off the US government.
I think the issue was, what was considered rape in Sweden was basically just being a misogynistic douche in other countries.
However, he would have known this well before going into the country, it's not like they created a new law just for him.
I doubt the US is so subtle as to use pirates. People seem to have these grand conspiracies about how the government is like a ninja...it's not.
They will simply send the police around and arrest him. Seriously, why are they going to bother with cloak and daggers for? This isn't a Bond movie. They will simply arrest him, and charge him with espionage charges since...err..that's sort of what he did?
Vladivostok, which is very close to Japan, and would be nearly impossible to not go through either South Korean or Japanese waters. Neither of which are friendly to him.
Sevastopol, Which requires going through the Turkey, and then either through the straights of Gibraltar or Egypt.
St Petersburg, Which requires passing through Denmark.
If I were in his shoes, I'd probably try to charter a Jet coming out of Vladivostok. If that wasn't possible, I think I'd choose the Sevastopol/Gibraltar route by sea.
http://thediplomat.com/2011/10/chinas-overhyped-submarine-threat/
>The Song-class vessel, displacing 2,200 tons, was close enough to hit the Kitty Hawk with one of its 18 homing torpedoes. None of the carrier’s roughly dozen escorting warships detected the Song until it breached the surface.
And:
https://www.youtube.com/watch?v=nqFVOL7mLd4#t=9m58sMy point was that if Snowden were to travel by plane then there is a high probability that it could be forced to be grounded and Snowden captured then sent to Gitmo.
But if he were to travel by submarine, he would be untouchable from the US Navy.
It's silly to think the US would get into a military engagement with Russia just to capture Snowden. At this point, he's not that valuable to either side, except as a propaganda tool. Hell, Putin would probably do a happy dance if the US were stupid enough to do something like that. The sabre rattling in the Ukraine has made him very popular - one can only imagine what a revived cold war rivalry would do for him; in the short term, at least.
Granted, a boat trip is longer, which is more time for things to (be made to) go wrong, but if a ship is traveling through international waters, are there any grounds for another country to board it and seize its passengers?
(With a follow up: is there a sea route between Russia and Friendly Country X which doesn't pass through waters claimed by another country?)