The 62-year-old spoke out as Dr Kelly's death was further shrouded in mystery - when one doctor claimed to have read the post-mortem report despite it having been kept classified after the weapons inspector's death.
Miss Wearmouth is Dr Kelly's first cousin and the only member of his family to speak publicly since renewed speculation about the circumstances his death.
She said: 'From the day I heard he'd died I had an instinct that there was something very unusual about it and I don't believe the official explanation.
'Looking back, was someone frightened that he was going to say more, that he had so much information?
'A man in his position would have been privy to a lot of things, and seen a lot of things, and I believe he was killed.'