An unnamed French man has been jailed for attempted rape without police knowing his real name or the identity of his victim.
The attacker, who was prosecuted under the assumed name Aurilien Cheyroux, was caught assaulting the woman in Holloway, north London in the early hours of 1 March.
Two passers-by heard a woman screaming for help as they were walking down Caledonian Road at around 2am.
They searched the area and found a woman lying on the ground with a partially dressed man on top of her, trying to rip off her clothes. He attempted to escape, but was caught by the witnesses and detained.
The woman left before the police could arrive on the scene, having said she was uninjured.
The attacker told police he was a French national called Aurilien Cheyroux, but French authorities said the information was incorrect, and were unable to establish his real identity.
"Cheyroux" was jailed for six years by Blackfriars Crown Court on 14 August, with the judge ruling that he should be deported once his sentence was served.
'Highly unusual case'
Det Const Kip Malek said: "This is a highly unusual case where we have been unable to trace the victim and the man who has been convicted is under an assumed name.
"Despite this we have been able to get a conviction and that is due to the brave members of the public who witnessed the attack and took it upon themselves to pursue this man and contact us."
"This incident should demonstrate to people that we take all offences of sexual assault very seriously and when they do occur, we do everything we can to bring the offenders to justice."
Det Insp Neil Smithson said: "I am still keen to ascertain his identity. Equally, if you were the victim of this offence please contact us - we have specially trained officers who can support you."
"I would urge anyone who has been the victim of sexual violence to come forward, safe in the knowledge that they will be listened to, the case will be thoroughly investigated and we will provide bespoke victim care depending on the individual's needs."