Joseph Barnett lover of Mary Jane Kelly.
He lived in Whitechapel.
He most strongly resemble's the F.B.I.'S Psychological profile.
Somebody answering his description was seen at the scene of every one of the murders.
Whoever killed Kelly must have been known & trusted by her as she allowed him into her home. (Her trade was plied in back alleys)
Barnett made a living from filleting fish.
It is well within the batting average of chance that Sickert sent at least one hoax letter but so did dozens of other People.