Let us say that something like this were to happen in Iraq in 2003. Paul Bremer has a job that is vaguely analogous to that of Pilate. Let us say Bremer were to appoint an Iraqi to the job of Minister of Law Enforcement but require that this person get Bremer's approval before executing anyone.
Let us say (hypothetically) that this Iraqi minister came to Bremer one day and said that a certain individual was guilty of a crime and deserved execution. Bremer looked into the matter and it appeared to him that the man was innocent, but a mob suddenly appeared and began chanting for the man's death, so Bremer acquiesced and executed the man.
Who would be held responsible for that execution? The Iraqi people or Bremer?
Bremer, of course, would be held responsible. The same should be said of Pilate. As the offical in command, Pilate should be held accountable for the death of Jesus, not the Jews.