Yes, definitely.
I don't dispute the extreme difficulty of the police's job here and do not, in the least, envy those faced with these decisions.
But...
The mistakes made were huge and, more importantly, were judged to be avoidable. Among other things, he was allowed to get on 2 buses when the police thought he was the suicide bomber and not one of the witnesses recalled hearing a warning that indicated that the armed men were police officers.
For some time after the error was known, a false account of the incident continued to be put out by the Met.
An innocent man died. His immigration status does not alter that one little bit despite the views of some to the contrary.
There was a time when, in a case anything like this, the top man would have wasted no time in resigning as a matter of principle.
Ian Blair must, absolutely must, resign without further delay.