From the Sydney Morning Herald:
Police suspects that only one bomb maker was involved but he had used sophisticated military explosives probably smuggled into Britain from the Balkans, and not home-made stuff. British police has had help from French police in determining the origin of the explosives. They are very worried by the nature of the military origin of the explosives. The bombs were very sophisticated.
Forensic pathologists believe the bus bomber could well be either holding the bomb or sitting on top of it. Experience in Israel found that suicide bombers usually had their heads decapitated by the blast, and a head was found on Bus No 30.