You've missed so many salient points, for example:-
1. For a decade, the police knew nothing about him - although he was raping dozens of people regularly, in central Manchester
2. University contacts/neighours said nothing, or noticed, anything. A guy living in a small apartment block, with numerous academic associates
3. Even his generous funder - UK academia - continued to finance him, because of his ability pass exans; a permanent student
Not a good police performance - but, most significantly, an insight into the ability of cheap drugs to take over your mind, and body.
This foreign chap, who we eagerly funded to live in the middle of one of our largest cities, simply got hold of a drug - which allowed him to rape, and make his victims forget.
And was discovered through happenstance....