The CPS report says it's both.It was a failure of the police not the CPS
It would help you if you researched the difference between the police and the CPS.
The CPS has the power and responsibility to push the police to go get more evidence or check again with witnesses. The CPS should have done so but failed to do so.
On the face of it, the allegations made were both serious and
credible; the prosecutor should have recognised this and
sought to “build” a prosecution. In particular, there were
aspects of what he was told by the police as to the reasons that
the victims did not want to give evidence which should have
caused him to ask further questions. Instead, he appears to
have treated the obstacles as fatal to the prospects of a
prosecution taking place.

