TWE - "He was that insane Andy, the police could not catch him, a very devious man."
Deviousness and insanity are not necessarily connected, you don;t have to have one to be the other.
Not sure if you are old enough to have been around when the Ripper murders took place - I was, and I remember it well.
For a start, police proceedures were nothing like as comprehensive as they are now. There was no internet, no DNA, no computerised records, and little sharing of information between different police forces.
Plus, the entire operation was completely derailed by a hoax caller, a Geordie who taunted the police and sent them off in completely the wrong direction, leaving Sutcliffe to kill three more times.
Sutcliffe was actually interviewed and released twice during the enquiries, and he was only caught in the end because of a dodgy numberplate, so it was actually complete luck that he was aprehended when he was.
Allowing for that context, devious as Sutcliffe may have been, he didn't have to work too hard to avoid capture.