Complex sentence: The Japanese prison initially refused to release her body, but eventually and reluctantly the prison released her body to Fry and Walter, principles of Ehwa Women's School and only after Fry and Walter threatened to expose this atrocity to the world.
Split into simpler sentences: The Japanese prison initially refused to release the corpse when Fry and Walter, principles of Ehwa Women's School, requested it. The prison released the corpse only, and reluctantly so, when Fry and Walter threatened to petition this atrocity to the world.