The body of Joan Francisco, a 27-year-old gynaecologist, was found wearing only knickers and a T-shirt in her flat in north-west London, on Boxing Day in 1994. She was strangled with a vacuum cleaner cord.
Following a lengthy police investigation, the Crown Prosecution Service ruled there was insufficient evidence to bring a prosecution, but now her family have brought a civil action against Anthony Diedrick, claiming assault and battery leading to her murder.
It is believed to be the first time a civil case has been brought against a suspect before there has been any criminal prosecution linked to the murder.
Patrick O'Connor QC, for the Francisco family, said Mr Diedrick, who was a former boyfriend from six years before, harboured a "violent and perverted obsession" for Ms Francisco which led to her death.
"That obsession intensified in the months before Christmas 1994 and reached a crisis on the day of her murder," he said.
Ms Francisco, who was always conscious of her personal security, had been due to fly out to California to visit her sisters, Margrette and Celia, on the day she died.
Mr O'Connor said that when Mr Diedrick heard she was leaving for the United States he assumed that she was leaving long-term or permanently.
"It is this belief by him that she may have been leaving the country for such a length of time that led to his harbouring a growing sense of crisis in his obsession and the need for some kind of dramatic confrontation or gesture on the morning of Boxing Day."
Margrette told the court that she met Mr Diedrick in the late 1980s when he visited Los Angeles with her sister and described how he "got into a seething rage - like he was going to erupt".
"It really shook me up and I was very disturbed by the anger and hostility he displayed just because of a difference of opinion," she said
Mr O'Connor said it was no coincidence that Joan was murdered only hours before her departure for the United States.
"Anthony Diedrick knew about her departure and seems to have imagined that he may never see her again. There is nobody else for whom that day and this hour had any such significance."
Mr Diedrick, a computer studies graduate, had a relationship with Joan which started in February 1987 and was ended by her at Christmas 1988.
The court heard that Mr Diedrick became obsessed with Ms Francisco.
On one occasion he smashed his way through a patio door and chased Joan and a male friend, who he threatened to kill, upstairs where they locked themselves in a room, the court heard.
Mr Diedrick told police that he felt compelled to go to the house and spoke in "apocalyptic terms" of how he had wanted to kill the friend and would rather die than go to prison. In 1994 he saw Ms Francisco in a nightclub and his obsession was revived. A week before her death he pushed a note for her through the door of her mother's house.
It said: "It's unlikely that we'll ever see each other or speak to each other again. It would have been nice if we could have had a last few words together."
Mr O'Connor said: "Those words speak volumes. Unless Tony Diedrick is thinking in apocalyptic terms from the point of view of his obsession he couldn't be writing those words."
Mr Diedrick claimed as an alibi that he spent Christmas Day night and Boxing Day morning at his flat before going to his mother's for the day at 10am. He was arrested in March 1994, but released without charge. The case continues.Reuse content