U.S.-Canadian environmentalist Paul Watson, 74, was detained based on a decade-old Interpol warrant that accused him of interfering with a Japanese whaling ship.

The founder of Sea Shepherd, Paul Watson had been detained since July on a 2012 Japanese arrest warrant, which accuses him of causing damage to a whaling ship in the Antarctic in 2010 and injuring a whaler.

Denmark rejected Japan’s request to extradite Canadian-American Paul Watson in a decision released Tuesday, freeing the anti-whaling activist after five months in a Greenland jail.