Ashley Olsen, the American found strangled and naked in her Florence flat, was killed by an illegal immigrant from Senegal she met in a nightclub, the prosecutor in charge of the case said Thursday.

The 27-year-old alleged murderer was arrested overnight after his DNA was matched to traces recovered from Olsen’s corpse and from a condom and a cigarette butt found in the flat, prosecutor Giuseppe Creazzo told a press conference in the historic Tuscan city.

Creazzo said CCTV recordings and witness statements indicated the suspect had met Olsen in the Montecarla nightclub in the early hours of Friday and accompanied her back to her flat.

The couple had sex but there was no indication that Olsen’s death resulted from an erotic asphyxiation game gone wrong, a theory widely mooted in the Italian media in recent days.

Press reports earlier put the suspect’s age at 25.

Creazza said Olsen had died as a result of strangling but had also suffered a double fracture of the skull, suggesting there had been a fight at some point after the couple had sex.

The prosecutor said the suspect, who had entered Italy illegally a few months ago, had “largely admitted” his role in the killing but said the investigation would continue to tie up all the loose ends.

He said it was possible that neither Olsen or the alleged killer “were entirely clear-headed” at the time of the murder but said that would not be clear until toxicology tests had established if either of them had taken drugs.