What's her sex life got to do with it?

From the moment Joanne Lees flagged down a lorry on a remote road in Australia's Northern Territory almost three years ago, she has been an object of suspicion. Sceptics still find it hard to believe that her boyfriend, the British backpacker Peter Falconio, was murdered by a stranger with a gun who then tried to kidnap her. Falconio's body has never been found, and eyebrows were raised when Lees told police that she had escaped from the killer's vehicle and hidden in the bush, waiting quietly until he gave up trying to discover her hiding place.

Last week, as she gave evidence in an Australian court, the lorry driver who came to her rescue provided a vivid account of the moment he spotted Lees in his headlights. Vince Millar recalled how he swerved, thinking for a moment that he had accidentally killed her. It was not, however, this further insight into Lees's ghastly experience that made headlines. The "sensational" development that excited the media was her admission, under aggressive questioning, that she had had a relationship with another man. An Australian lawyer, Grant Algie, bombarded Lees with questions about a man identified only by his first name, Nick, demanding to know whether she had had an affair with him. "During the time you were living in Sydney with Peter you were having an affair, a sexual relationship over a period of weeks, with Nick. Yes or no?" he demanded.

Anyone unfamiliar with the case might reasonably have concluded that it was Lees who was on trial at Darwin magistrates' court. In spite of protests from the prosecution, Algie was allowed to pursue his line of questioning, forcing Lees into an admission that she had concealed the relationship from Falconio. So what was Algie trying to prove? That Lees was somehow complicit in her boyfriend's murder? There are easier ways of ending a relationship than staging an abduction, and in any case it is Algie's client, a 45-year-old mechanic from Western Australia named Bradley John Murdoch, who faces charges of murder, assault and attempted abduction.

Lees has not been accused of anything, except through innuendo and biased reporting. Journalists loathed her from the beginning, when police in Alice Springs revealed her story and she refused to give interviews. The moment it became apparent that she would not provide a tearful account of the crime to any journalist who demanded it, the insinuations began to appear: that she was too composed, too sure of herself, and that there was something fishy about her reluctance to answer questions from the press. Newspapers were further enraged when she gave a television interview to Martin Bashir, in exchange for a reported £50,000, and last week's gleeful headlines are their revenge.

They are also, to anyone who has followed rape trials, wearily familiar. Lawyers have spent years devising ways of getting victims' sexual histories into court, because juries do not like women who have had sex with more than one man. Now that it has been made more difficult to go on such fishing expeditions in British courts, they resort to dragging in other irrelevancies, such as the fact that a woman has been prescribed anti-depressants. Sluts or nuts: your average defence barrister is not fussy about the methods he uses to damage a woman's reputation, as long they undermine her credibility as a witness. And that is what Murdoch's lawyer was up to last week, successfully switching everyone's attention from his client to the woman he is alleged to have assaulted.

Not long after my first visit to Australia, to speak at a conference in Adelaide, the victims of a serial killer were discovered in the vault of a local bank. In Perth, where I am an associate professor, friends still talk fearfully about a serial killer who has never been apprehended. Backpackers are favourite targets, and Lees and Falconio are not the first people to have been attacked on the deserted roads that cross Australia. I would think twice about stopping in the outback, as Lees says she did when she and Falconio passed a grass fire by the side of the road. "It may be a trap," she told him. Now she has fallen into another, set by lawyers and the press, who judge a woman's credibility by her sex life and her willingness to behave like their idea of a victim.