The tragedy emerged on the day a man was given five life sentences at the Old Bailey for the double rape on Boxing Day two years ago and the rape of a 17-year-old schoolgirl 10 months later. The court heard that the mother and her daughter were staying with relatives and had gone to bed on Christmas night in 1996.
It was later confirmed that the woman, 20, who was found in Kensington Gardens last Tuesday had died from drowning. There were not believed to be any suspicious circumstances.
The woman had a history of psychiatric illness and left her mother's home early in November just before the rape trial started.
Defence counsel for William Kenealy, 25, of Northolt, north-west London, had asked for mercy and denied his client was "a monster". Kenealy had pleaded not guilty to the rapes.
DNA evidence from both crimes linked them to Kenealy. Police plan to interview him about two other rapes. Judge Ian Davies told Kenealy: "I am satisfied your conduct has manifestly perverted tendencies and while at large you will remain a danger to women for an indefinite time."