The London Mayor must have known this kind of attack was a distinct possibility since he was elected. With ample time to reflect on his wording, this would have been a good oppoutunity to show how a practicing Muslim whose job is managing one of the largest democratic cities in the world would be able to show the world that a walk along that bridge is possible. 
He could have said that as a Muslim, he denounces this kind of attack in the name of his religion. He could have called on mosques to discourage and report. He position is unique. 
 But he played it safe and was afraid to make a difference.
May and Trump understand. This writer, representing his own country can not even bring himself to speak the language needed as a first step. It makes his logic, of what to do as a next step, complete mute.