Relevant to the bombings in London and the kind of thought and language that enables people to justify such actions after deciding they want to commit them*:
Muslim scholars declare that only religious authorities can issue fatwas (Al Jazeera).
The three-day meeting in Amman, which ended on Wednesday, has for the first time gathered representatives of eight Sunni and Shia Muslim schools of thought.
The Muslim world's top scholars have agreed that fatwas, or religious edicts, should only be issued by clerics with religious authority.
They all also agreed that followers cannot label other Muslims as "apostates", something groups in Iraq have done to justify attacks against Iraqi police and civilians.
*I phrase it this way because this appears to be how it works much of the time. See The Anatomy of Motive by John Douglas.