Regarding the hoax tapes/letters and given lots of other clues,police bosses shud have twigged much earlier that they were a hoax.
In one of the letters the writer failed to make reference to one of the murders when their had bn two in quick succession and before he wrote it.Boasting and taunting as he was he never mentioned it.
George Oldfield definitely made it a personal vendetta and wrongly placed all his eggs in one basket.
Officers of senior rank and experience should have known far better and completed the jigsaw far sooner.Sadly,it came too late for many more victims.