'I killer her by mistake,' he told interrogators after arrest - and prosecutors now think theory of kinky sex game was wrong

Diaw claims he punched her when she told him to leave because her boyfriend was coming back and denies strangling her

Artist was found dead in Florence apartment by her boyfriend on Saturday; she had two fractures to the skull and was strangled with a USB cord

He has confessed to murdering her to officers who arrested him because of a DNA match to used condom and cigarette found in apartment

Senegalese Cheik Tidiane Diaw, 25 is accused of aggravated murder of Ashley Olsen in her Florence apartment

Victim: Ashley Olsen, 35, was found dead in her apartment in Florence, Italy on Saturday by her boyfriend

An illegal immigrant has confessed to killing American artist Ashley Olsen in her Italian apartment, who was punched and strangled with a USB cord in what police say was a jealous 'drug-fueled' frenzy

Cheik Tidiane Diaw, 25, told officers he strangled Olsen after the pair had sex when she told him he had to leave because her boyfriend was coming back.

The Senegalese man was caught because of DNA evidence from a used condom and cigarette found in the toilet - which he had tried to flush away unsuccessfully.

Italian police said they had to swoop on him quickly because they feared he was about to flee Florence.

The chief prosecutor said that the alleged murderer had initially given a false alibi to police when he was first questioned. He was freed but then re-arrested when his DNA was matched.

Olsen, whose funeral will be held in the Italian city tomorrow, suffered two fractures to the skull and was strangled with a USB cord.

She met her alleged killer at the Montecarla club, notorious for sex and drugs, and left together at 5.30am, when they went to her apartment.

The victim did not leave the club alone, as previously thought, and Diaw's confession suggests that the police's initial finding of a 'consensual' kinky sex game before her death may have been wrong.

Olsen's body was found on Saturday by her boyfriend, who was concerned he had not heard from her. He desperately tried to revive her but it was too late. Her beloved dog was at her side in its own urine and feces, and is now being cared for by her family.

At a press conference today in Florence, the chief prosecutor Giuseppe Creazzo said: 'We think sexual relations occurred before the homicide, not during it.

'We do not know whether they took drugs together before she was killed but we are awaiting the results of analysis,' he added.

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Accused: Cheik Tidiane Diaw, 25, is being held in Italy on suspicion of strangling Olsen after leaving a sex club with her in Florence on Friday.

Victim: Olsen died when she was strangled with a USB wire or cord, an autopsy has found

Police found a used condom and cigarette in the victim's toilet which helped identify the suspect.

The killer had attempted to flush the condom and cigarette down the lavatory, investigators said, but the flush had failed and the objects were recovered by the forensic team.

Diaw is also alleged to have taken her phone from the scene of the crime and placed his own SIM card inside it.

He told police that her death was the result of a fight after having consensual sex.

According to police, he told interrogators: 'She told me to leave and that her boyfriend was coming and she pushed me to the door.'

He then said that he punched her in the head, screaming 'you have treated me like a dog'.

Olsen fell back, got up and tried to push him away. He shoved her back and she fell and struck her head, fracturing her skull in two places.

But he denied intentionally strangling Olsen, insisting that the marks around her neck were created when he tried to pull her up.

'It is likely that the killer and victim were not lucid at the time of the murder,' The Chief Prosecutor, Giuseppe Creazzo, said.

'We have reason to believe that they took substances that made them not lucid. Alcohol for sure, maybe other substances.

'We will know more when the drugs tests on Ashley come back.'

Illegal: Diaw had entered Italy as little as two months ago illegally from Senegal and posted pictures on social media suggesting he was happy to be there. Prosecutors said they did not believe believe he knew Olsen before their night together

Arrest: Provincial police chief Raffaelle Micillo chief prosecutor Giuseppe Creazzo and Flying Squad chief Giacinto Profazio spoke at a press conference today, revealing they had arrested Cheik Tidiane Diaw

Diaw told police that he killed her 'by mistake', sources said.He has admitted that he was responsible for her death, but that it was an accident.

'I pushed her and she hit her head,' he told police. 'The signs of strangulation are from when when I tried to pick her up.'

The autopsy revealed that the 35-year-old victim had suffered a blow to the skull, which was found to be fractured in two places.

Creazzo, said that police have so far only been investigating her strangulation.

The revelation of this new kind of violence suggests that the killing may have been more aggressive than previously thought, he said.

'It may not have been an erotic game after all,' he said.

He also said it was likely a drug-fueled one-night-stand gone wrong, as the two met at the notorious nightclub Montcarla just hours before Olsen was killed.

'We also cannot find any evidence that they knew each other before that night,' he said.

Police were forced to close in on the suspect 'like a sea urchin' because of fears that the intensity of the media coverage would cause the suspect to flee Florence, the chief prosecutor has said.

If Diaw had escaped, he added, it would have been almost impossible to trace him as he was in Italy illegally and had only been in the country for a matter of weeks.

He also revealed that Diaw, 27, had given a false alibi for the night of the murder, claiming that he had been at home when he was first questioned after being identified by eyewitness and CCTV evidence.

'Because of media coverage in recent hours, there was a risk of the suspect fleeing and compromising the investigation, so we closed on him like a sea urchin,' said Giuseppe Creazzo, the chief prosecutor.

Grief of a father: Walter Olsen, Ashley's father arrived with two women and the family's lawyer Annamaria Gallo (right) at the city morgue. They will hold a private funeral for her tomorrow

Preparations: The arrest of Diaw has cleared the way for the release of the dead woman's body to her family at the city morgue. They will hold a funeral service for her tomorrow

Search: Forensic officers spent all day at Ashley Olsen's apartment. Police have identified an apparent suspect, seen on CCTV with her close to the building

Illegal: Diaw was from Senegal in West Africa but had arrived in Italy as little as two months ago

Investigators had questioned Diaw in the days before his arrest and taken his DNA, which allowed the forensic team to confirm that he had been at the apartment, he said.

'Thanks to the strategy of the investigators it was possible to compare the DNA of the 27-year-old to the biological traces found in the apartment because in recent days he had been questioned by the prosecutor's team and he gave a false alibi, claiming that on the night of the homicide he was at home,' he said.

It also emerged that Diaw has more than one sibling in Italy, at least one of whom was in the country legitimately. Their identities have not been released.

Ashley Olsen's body is resting at the Careggi hospital chapel in Florence. It will remain there until 3pm tomorrow, when it will be taken to the Basilica di Santo Spirito for the funeral.

Police confirmed that the suspect had entered Italy illegally, and was staying with his brother, who is in the country legitimately.

He had been earning money by handing out flyers for a nightclub.

The suspect is being held in Sollicciano jail in the city, having been arrested at midnight on Thursday, after being under observation for several days.

He was questioned for four hours and is cooperating with police.

Flying Squad chief Giacinto Profazio, the police chief who also led the investigation into the murder of British student Meredith Kercher in Perugia in 2007, said: 'I would like to congratulate the forensic and detective teams for their efficiency of their investigation and its very quick resolution.

'Florence remains a very safe city and this type of crime happens everywhere in the world,' he added.

'Investigators were very quick to resolve the case and arrest the subject.'

As the central heating was turned up in the apartment, investigators found it difficult to pinpoint the time of death, but their best estimations place it between seven in the morning and one in the afternoon on Friday

Tributes: Flowers have been left on the door step and tributes have been scrawled round the doorway

Forensic investigators spent six hours inside Olsen's flat, searching for DNA traces that would link Diaw to the crime.

He had fallen under suspicion based on CCTV footage, which appeared to show him together with Olsen outside the apartment in the early hours of Friday morning, the last time she was seen alive.

Police have indicated that the CCTV footage and eyewitness testimony alone may be enough to secure a conviction, but conclusive DNA evidence would greatly strengthen the case.

The revelation that the suspect is an illegal immigrant is likely to aggravate social tensions across Europe following the sexual assaults that took place on the continent over the New Year period.

This morning, a forensic team returned once again to the scene of the crime to continue their painstaking, fingertip search.

Evidence of alcohol was found in the flat, but drug tests have yet to be concluded, police said.

An autopsy revealed that Olsen had sex before she was killed, and there were no signs on her body that she had put up a fight.

There was also no indication that she had struggled to remove the cord around her neck, and no evidence of forced entry or struggle at the apartment.

Olsen was found by her boyfriend on Saturday after failing to get in touch with him. He tried desperately to revive her but she was already dead.

Detectives have now pieced together a timeline of her last hours which shows that she spent time at Montecarla, a sleazy bar and nightclub which has been repeatedly linked to drugs in the early hours of Friday morning.

Painstaking: The officer in charge of the homicide squad said the search would take some time

Speaking out: Walter Olsen, pictured in Florence, said: 'She was a beautiful and creative young woman with a happy, exuberant and generous soul. We are heartbroken that she was taken from us.'

Couple: Federico Fiorentini (left) and Ashley Olsen (right) were together for seven years. Police say he is not a suspect. He found her body and tried to revive her with CPR.

The victim was with a group of friends and the atmosphere was 'tense'. After an altercation, her companions got up and left Olsen at the club.

Olsen then met a man.

A witness saw them together and described the man to the police, and the two were captured on CCTV walking together to Olsen's chic apartment.

As the central heating was turned up in the apartment, investigators found it difficult to pinpoint the time of death, but their best estimations place it between seven in the morning and one in the afternoon on Friday.

Investigators have not disclosed whether drugs were found in the apartment.

Olsen's mother was planning to fly to Italy overnight and is expected to arrive today, where she and the victim's father, Walter Olsen, will say their final goodbyes and decide where she will be buried.

Alessandro Ausenda, chief of the homicide squad said as he left the scene of the crime yesterday: 'The forensic investigation will take a long time.'

Witnesses at the club told Daily Mail Online she had been there and arrived with friends but did not leave with him.

Giulia, a bartender at the Montecarla who saw the victim at the club said: 'She was a chilled-out person, I'd even call her delicate.

'She came into the club at 4:30am, had a drink and left at 5:30am. She was tense and before leaving she had a difference of opinion with a female friend.'

Detectives confirm that they have cleared entirely her boyfriend, Italian-American artist Federico Fiorentini, 42, has a watertight alibi.

The development in the investigation came after Walter Olsen, an art professor in the same city who lives round the corner from his daughter's apartment, paid tribute to his 'beautiful and creative' daughter and said he had faith in the murder investigation.

The 35-year-old was last seen alive at the Montecarla club, an insalubrious members-only establishment

Key to investigation: The Montecarla club 'is a place where you can find anything you are looking for, sex, drugs, transexuals,' said a woman in a nearby bar

'We are devastated that our precious Ashley has passed away resulting from a horrible and senseless crime,' he said.

'She was a beautiful and creative young woman with a happy, exuberant and generous soul, and she loved her life in Florence, in San Frediano.

'We are heartbroken that she was taken from us.'

After making an appeal for his privacy to be respected, he added: 'We have faith that the perpetrator will be found and sentenced. We thank everyone for their loving thoughts and prayers.'

Olsen – who is a professor of architecture, design and drawing at Bianca Cappello Art Academy in the city – has not been seen in public since Monday.

That day he laid a bouquet of flowers outside his daughter's apartment flanked by police officers and officials from the American consulate in Florence.

He bowed his head and knelt for a few minutes in silence before placing the flowers on her doorstep.

For the past few days he has been enduring an agonizing wait for his daughter's autopsy to be over so that he can 'hug [his] daughter one last time'.

Her boyfriend is also said to be devastated. He is being comforted by his mother and sister, who both live in the city.

In charge: Alessandro Ausenda, chief of the homicide squad (center) said as he left the scene of the crime today: 'The forensic investigation will take a long time.'

The victim's beloved dog, Scout, was present when she was murdered and was found in great distress, surrounded by his own urine and feces, when the body was discovered

On Saturday, concerned by the fact that Olsen had not been seen for days, Fiorentini persuaded her landlord to open the door to her chic apartment.

There he found her dead on her bed – which was raised on a mezzanine level – wearing nothing but her socks. Her beloved pet dog, Scout, was in a state of great distress, surrounded by his own faeces and urine.

Fiorentini panicked, lifting Olsen's body down onto the floor and desperately applying CPR. As he later explained to police, in the process he sustained scratches to his knuckles.

He telephoned an ambulance, and police were alerted.

'I thought I might be able to save her,' he told friends. 'I loved Ashley and I will absolutely find who killed her. They will pay for what they did.'

Her best friends also released a moving tribute to the victim.

'We are bereft and numbed by what has happened,' the statement said.

'This is horrific and unimaginable… Our thoughts and love go to Ashley's father, mother, and sister, and to all of her family.'