Ahhhh You've just wandered into Ray Dart territory.
There are three possibilities. The most likely suspect probably "just stopped" murdering when he had killed his own womanfriend. The other two possible murderers probably left the country, one of them back to America.
We'll never know, though it's fun to conjecture.
He probably underwent the world's first gender re-alignment surgery (performed by Dr Jekyll) and married Mr Hyde. This satisfied his (now her) lust to kill and he never offended again; but when Mr Hyde (whom Dr Jekyll had managed to keep in the dark about Jack's (now Jacqueline's) real identity, learned the truth, he went on a murder rampage of his own.
Perhaps he met his match. The next potential victim killed him off.
Some suspect he was in the royal family....today he would write a book
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