Is this Jack the Ripper's ripper?

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Above left is Welsh surgeon Sir John Williams who has long been suspected of being Jack the Ripper. Above right is a knife that Sir John's great-great-great-great nephew, Tony Williams, found that he claims is the Ripper's weapon. The story is in his book, Uncle Jack - A Victorian Mystery. From The Telegraph:

He found the blade among a stash of possessions left by the Welshman, including three glass slides which contains smears of a uterus.

Mr Williams said: ''Why would he leave this behind? I am convinced that this is the knife used by Sir John Williams to murder those women.

''It is widely know that the person who carried out the killings would have had significant medical knowledge.
''Sir John Williams was an accomplished surgeon and routinely performed abortions on women. He held surgeries all over London at the time of the murders."

He added: ''Dr Thomas Bond, a pathologist who examined the body of Mary Kelly, said the ripper had used the same six inch knife in all the murders.

"Jack the Ripper: Is this six-inch knife used by Victorian serial killer?"