Ms Francisco's elder sister Celia said that she wrote a warning letter to her in December 1988, six years before the 27- year-old gynaecologist was found strangled with a vacuum cleaner cord at her flat in St John's Wood, north-west London.
Celia, 33, who is based in the United States, wrote that she had heard some very disturbing things from their mother about Joan's then boyfriend - "the infamous Tone" - and an incident with a broken light-bulb.
It went on: "It seems to me he is a walking time bomb and honey, your time is running out. Don't forget he is from an extremely [underlined] violent background which has obviously had a lasting effect upon him, plus the incident with his girlfriend's nose. So why shouldn't he hurt you? It seems to be in his nature."
She told Joan that she should count herself lucky that the glass didn't catch her eyes. "Is the end of your medical career worth it for Tony Diedrick? ... does company and convenience outweigh the possibility of serious disablement? Think about it." Celia added that Joan was attractive, intelligent and articulate and should not sell herself short.
The letter, which was found among Ms Francisco's property after her death, was read out in court after Mr Justice Alliott rejected objections by Mr Diedrick's counsel, Ronald Thwaites QC.
Mr Diedrick, 38, who allegedly stalked Joan for months out of a "violent and perverted obsession" before killing her, is fighting an unprecedented civil action brought by the Francisco family. In what is thought to be the first civil action taken against someone when there has been no criminal prosecution connected to a murder, they are seeking up to pounds 50,000 compensation for alleged assault and battery.
Mr Diedrick, who was in court yesterday, was arrested in March 1994 and released without charge. But the family's counsel, Patrick O'Connor, says there is compelling circumstantial evidence which "pointed inexorably" towards his guilt.
Celia Francisco said that while her sister and Mr Diedrick were going out, she had arranged a job for him in America. "He was ... socially maladjusted. I would say he wasn't that trusting ... However ... if he felt he trusted you, he would become somewhat obsessive over you."
Ms Francisco said that she learned after writing the letter that Joan and Mr Diedrick had split up. After an incident in which Mr Diedrick broke into the family home in Acton, in February 1989, Joan didn't want anything to do with him.
"She feared for her life ... She had come to the decision that they were at the end of the relationship and it was final, However, Mr Diedrick didn't want to accept that."
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