That, too, was removed following a complaint from Ms Lecic that it was also a picture of her. Individuals who had become friends on Facebook with ''Amina Arraf'' then emerged to say that as many as 200 separate pictures had been posted on that site, some of them tagged and commented upon as if they were of Arraf - all were in fact of Ms Lecic.

Separately, a young woman from London, Jelena Lecic, had seen the media coverage of Arraf's kidnapping and contacted the media to say the pictures published around the world were not of an Arab lesbian, but had been taken from her own social media sites. The Guardian's website removed the photo, taken from a Facebook page calling for Arraf's release, and replaced it with an image that had been emailed directly to the Damascus correspondent by the person claiming to be Arraf.

No one in the Syrian lesbian and gay community seemed to have heard of her, and some details - such as when she wrote that secret police who had come to arrest her left after her father stood up to them - did not ring true.

On Monday, a post appeared on the blog signed by Arraf's cousin, Rania O Ismail, saying the activist had been snatched by security forces from a street, prompting headlines around the world. That is when the questions began. Andy Carvin, a senior strategist at the US broadcaster National Public Radio, who has become a key hub of Twitter contacts throughout the Middle East, wrote that he had been contacted, separately, by Syrian sources who said they had doubts about some of the details in the blog.

So at least some of the details on the blog were lies. Were any true? The US embassy in Damascus knew of no one called Amina Abdallah Arraf al Omari among the 4000 American citizens in Syria, nor of any young woman fitting her description who had been arrested. Searches of public records in Virginia, where the blogger said she was born, or Georgia, where she claimed to have gone to school and university, revealed no one by her name or the name she gave for her mother.

Despite the efforts of reporters, bloggers and internet and Twitter users, no one has been identified who has ever spoken to Arraf face to face. Sandra Bagaria, a French Canadian, had exchanged more than 500 emails with her, but on the one occasion she tried to speak to her in person she got no answer.

Is it a cynical hoax? Days after the mysterious post by Rania O Ismail, concrete evidence that it is fiction is absent. Even the fake photos and apparently false names are not, in themselves, proof the story is a lie. More than 10,000 people are thought to have been arrested by Syrian police since the uprising began, and if Arraf is not being mistreated in custody, as many have said, there are plenty like her who are. It is common for activists to use false names to obscure their identities.

But what remains, which means the mystery will not go away, is an absence. Why has Rania O Ismail, who according to a Facebook page and other social media sites is based in the US, not updated what she knows, given the internet storm over the blog?

But if the Gay Girl in Damascus is a hoax, it is an elaborate one. Cached pages on social media and dating websites suggest ''Amina Arraf'' has an internet identity dating back at least to 2007. Online friends on various sites say they have corresponded extensively, always by text, with someone they believe to be Arraf. Several of the pictures of Ms Lecic on the faked Facebook page were uploaded there last year or earlier, according to those who have seen them.