Reeling from the worst attack on American soil since 9/11, the US authorities believe at this stage that Omar Mateen was probably a deranged lone gunman who simply took the Isis name as a badge rather than being a trained operative of the group. “The most difficult type [of attacks] are the self-radicalised, lone wolves,” says Frances Townsend, former homeland security adviser to George W Bush when he was president. “It is easier to identify and intercept attacks where a terrorist group has direct operational control than it is to intercept self-radicalisation.”