He was the son of Rudolf Hess. He was also an outspoken critic of the investigation into his father's death, which he believed was a cover-up. He maintained that the British Secret Intelligence Service (SIS) had murdered his father in order to prevent his parole—which he believed to be imminent—because the British government were afraid that his father, if allowed to speak freely, would reveal embarrassing information about British actions during World War II. In 2007, however, documents demonstrating British support for Hess' release on humanitarian grounds and their campaign against steadfast Soviet opposition to his release were published