A UN probe into the assassination of former Lebanese Prime Minister Rafik al-Hariri is reportedly about to take a surprising new twist.Hariri was killed in February 2005 after a massive explosion in the centre of Beirut hit his motor cade. Revelations in Spiegel Online allege the UN tribunal now believes the Islamist group Hezbollah was behind the blast. The publication claims investigators are refusing to make the fresh evidence public. The inquiry had initially placed responsibility for the attack at the door of the Syrian security forces and high ranking Lebanese officials. The establishment of a UN special tribunal with a budget of 40 million euros was supposed to provide certainty over the murder. However, the assassination of Hariri, who was also a billionaire construction magnate responsible for helping to rebuild Lebanon after years of civil war, has been a source of wild speculation in the Middle East — al-Qaeda, Israel and Iran have all come under the spot light.