British tourist: I saw intoxicated Scarlett shortly before death

A British tourist has stepped from the shadows to reveal he saw the murdered teenager Scarlett Keeling lying on a Goan beach with a man on top of her hours before her partially naked corpse was discovered.

Having gone on the run fearful for his life after the teenager's death a month ago, Michael Mannion has now told how he saw a local barman, Samson D'Souza, in the compromising position. He had previously seen Scarlett stagger into the bar, apparently intoxicated, and start talking to Mr D'Souza and some other men. "I was told then by another local to stay away and not to say anything," he said.

Ms Keeling's family has long been aware of the existence of Mr Mannion, but also knew that he had fled the resort of Anjuna Beach apparently after receiving threats. The family's lawyer, Vikram Varma, said he believed Mr Mannion was now preparing to give his testimony to detectives. "He is definitely a genuine witness," said Mr Varma. "He is preparing to make himself available to police."

Scarlett's body was discovered on 19 February on the beach close to a bar called Lui's where Mr D'Souza worked. Police initially said her death was an accidental drowning but her mother, Fiona MacKeown, insisted her daughter had been raped and murdered and demanded the police order a second set of post-mortem tests. Those suggested Scarlett's death was "homicidal in nature".

Mr D'Souza and another man, Placido Carvalho, were detained by police last week and accused of forcing her to take a cocktail of drugs before they sexually assaulted her. In documents placed before the courts, police have claimed that Mr D'Souza, 29, has admitted raping Scarlett, after feeding her with drugs, and then dumping her body. The police say she subsequently drowned.

Mr Mannion, 35, from London, told the BBC that he saw Scarlett enter Lui's bar at around 3am on 18 February and watched her stumble while she spoke to three local men. She then came over to talk to him and revealed that she was just 15.

"Before she left the bar she said she had taken drugs, but she didn't say where they'd come from," said Mr Mannion. He said he saw Scarlett leave the bar at 5am with a man.

When he left the bar shortly afterwards, he saw the man Scarlett had left with driving off on a motor scooter. As the man pulled away, he could see, in the scooter's headlight, Mr D'Souza lying on top of Scarlett. "I was in a complete state of total panic, shock. I got on my bike and I rode off," said Mr Mannion. "Initially I said nothing, I did nothing. Then two of the people working in the [bar] were called in for questioning. I was told then by another local to stay away and not to say anything."

Ms MacKeown, who was away from Goa at the time of her daughter's death and who has been accused of negligence, hopes to return to the UK this week to bury Scarlett at their home in Bideford, Devon.