There was speculation Riggi, who killed her three children in 2010 at their Edinburgh home, had committed suicide after she was found dead in her room at the secure Rampton Hospital in Nottinghamshire last week.However, a Nottinghamshire Police spokeswoman said: "A post mortem examination has concluded that her death was a result of natural causes. There are no suspicious circumstances."
Riggi was serving 16 years in prison for culpable homicide. She had stabbed children Austin and Gianluca, both eight, and Cecilia, five, following a break-up with her husband. She then set off a gas explosion before leaping from the balcony in an apparent suicide attempt.
She was held in Cornton Vale Prison, Stirling, before being transferred to Nottinghamshire last year.
A woman is to go on trial in June accused of slashing Riggi with a razor while in Cornton Vale. Angela Hamilton, 40, is alleged to have struck Riggi in her face and head with the razor in November 2011.