The My Cousin Vinny star travelled to Italy to unearth secrets about her ancestors for Who Do You Think You Are? and she admits she turned investigator when she initially discovered her womanising relative had been murdered.
The actress examined church and state records to find out if the legend that her great-grandfather was shot dead in a bar over a gambling debt was true.
Tomei uncovered the fact that his cause of death was listed as an illness.
She says, "The mystery still remains between the story of this murder and then this supposed illness. That still all seems suspect. So I'm just looking for any other kind of records that could connect those dots."
Tomei's TV investigation airs in America on Friday night (10Feb12).