Boris Nemtsov had criticized Putin in a radio interview hours before he was murdered in Moscow on Sunday.
The move is part of a wider shift toward empowering Japan in military and security matters.
A Brookings Institution study has found that ISIS supporters are adept at getting the group's message social media traction.
The attacker Kim Ki-jong had made seven visits, organized by the unification ministry, to the North between 1999 and 2007.
By Thursday night, the documentary's original link posted by the BBC had been viewed over 100,000 times.
ISIS militants had demolished ancient statues at the Mosul Museum last week.
A letter, signed by eight Republicans and three Democrats, calls on Obama to arm Ukraine in its fight against pro-Russian rebels.