FLORENCE, Italy -- Italian prosecutors on Thursday laid out evidence collected against a key suspect in the death of an American woman who was strangled and suffered deadly head trauma in her Florence apartment: They said a Senegalese man she met at a disco had left "decisive" DNA traces on a condom and cigarette butt at her home and was using her cellphone.

Cheik Tidiane Diaw, a 27-year-old who had arrived in Italy from Senegal in recent months, admitted under questioning he and Ashley Olsen, 35, had fought violently after a night of drugs and sex but denied strangling her and said he never intended to kill her, his lawyer said.

Diaw was arrested early Thursday at his brother's apartment and is being held on suspicion of aggravated homicide, Florence chief prosecutor Giuseppe Creazzo told a news conference.

Street-mounted security cameras and witnesses reported Diaw and Olsen had left Florence's Montecarla nightclub in the early hours of Jan. 8 and went to her home.

Once there, they had consensual sex. But sometime afterward, Olsen's skull was fractured in two places with blows so violent they alone could have killed her, Creazzo said.

She subsequently was strangled, apparently with a cord or rope.

Olsen's naked body was discovered the following day by her Italian boyfriend, who asked the apartment's owner to let him in because he hadn't heard from her in a few days, authorities have said.

Diaw acknowledged under questioning he and Olsen had consensual sex, were drunk and had been high on cocaine, his lawyer Antonio Voce told The Associated Press.

But Diaw denied strangling her, left her alive on her bed and never intended to kill her, Voce said.

Voce said Diaw told investigators they had fought when she tried to push him out of the apartment, fearing her boyfriend would be arriving.

After being pushed against the door, Diaw responded by punching Olsen in the neck and then pushing her to the ground, where she hit her head, Voce said.

He said Diaw helped her to the bed and left.