 This detail raised the suspicion of a Sunderland detective inspector that the Wearside Jack evidence was a hoax (as the writer of the letter made no reference to this crime) and submitted a report to the Northumbria police in September 1979, but was ignored.One coincidence between Harrison's (then falsely suspected) killer and Wearside Jack was the secretion of their B-group blood cells in their saliva and semen, retrieved from her murder scene and from the gum of one of the letters, a quality shared by only 6% of men.It was this which was taken as definitive proof the Yorkshire Ripper was the same man as had sent the letters and the tape.