Last Updated Jan 14, 2016 2:09 PM EST
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 that he and Ashley Olsen, 35, had fought violently after a night of drugs and sex but denied strangling her and 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 that 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 was subsequently 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 that he and Olsen had 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 that 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.
Diaw helped her to the bed and left.
"He felt taken advantage of," Voce said. "She was still alive when he left."
Creazzo said Diaw had offered "substantially admissive" testimony in response to the accusations during a preliminary interrogation that lasted until 4 a.m. Thursday. Diaw has not been charged.
Police detained Diaw after DNA analysis came back from a used condom and cigarette butt found in Olsen's toilet, as well as biological samples taken from under her fingernails that belonged to Diaw, Creazzo said.
Investigators matched that evidence with a DNA sample taken from a cigarette Diaw smoked while being questioned at the police station, prosecutors said. They said the tests were conducted in "record time."
Diaw had also taken Olsen's cellphone, put his own SIM card in it and used it, Creazzo said.
"We have gathered serious indications of guilt against him," Creazzo said, adding however, that a judge must confirm the arrest.
Creazzo said Diaw had arrived in Italy illegally a few months ago to join brothers who had been there for some time. He told investigators he was working odd jobs, handing out flyers for local nightspots.
Creazzo said the investigation continues but that no other suspects were at the scene of the crime. He said investigators had reached "a great point" in the investigation following the "decisive proof" from the DNA analysis.
Authorities have been at pains to not jump to conclusions in the case, given the intense international media interest that harks back to the Amanda Knox case. Knox and her Italian boyfriend were convicted in the 2007 death of her British roommate. They were then acquitted, convicted again and finally exonerated after an eight-year saga that cast a poor light on Italy's police and investigative magistrates.
Creazzo seemed almost apologetic that he hadn't been able to provide more information before Thursday's arrest. But he said that since Diaw was in Italy illegally, police would have had little hope of finding him if he had been tipped off that police were closing in on him and tried to flee.
CBS News correspondent Allen Pizzey reported that Olsen had been living in Florence for about three years and was described as well-known and popular in her neighborhood.
She came to Florence to be near her father, a professor at a local design institute, and start life over after a divorce.
A prolific user of social media, she even posted a line from the book and movie "Eat, Pray, Love" about an American woman who came to Florence to find herself.
But her last post was of a graffiti with the words, "Kiss me hard before you go."
Late Thursday, family members gathered at the chapel of the morgue where her body was being held.
A funeral was scheduled for Friday afternoon at the Santo Spirito church in Florence's Oltrarno neighborhood where Olsen lived. Friends say the church steps were a favorite hang-out spot for Olsen, her friends and her beloved beagle, Scout.