The murder of a young Sicilian woman by a stalker in broad daylight has sent shockwaves across Italy, where 11 women have been killed since the start of the year.

University student Sara Campanella, 22, was killed by an acquaintance on Monday afternoon in the Sicilian city of Messina.

Witnesses told media that they saw a man – later identified by prosecutors as 27-year-old Stefano Argentino – walk up to Ms Campanella and stab her on the street. She tried to get away and screamed “Stop it, let me go, stop it,” before collapsing, they said.

A passer-by who reportedly heard Ms Campanella’s screams tried to chase the attacker, who managed to flee.

Ms Campanella died on her way to the hospital. Mr Argentino was arrested a few hours later in the nearby town of Noto.

Raffaele Leone, Mr Argentino’s lawyer, told Italian media on Wednesday that his client had admitted the charges against him, but had not explained why he had attacked her.

“I can’t say if he’s remorseful, he’s quite closed up,” Mr Leone was quoted by Ansa news agency as saying.

The Messina prosecutor, Antonio D’Amato, said that Stefano Argentino had “insistently and repeatedly” harassed Sara Campanella since she started university two years ago. She was studying to become a biomedical technician.

One of her friends once had to intervene when Mr Argentino kept complaining that Ms Campanella no longer smiled at him, Mr D’Amato said.

But he added that Ms Campanella never went to the police as she did not feel that Mr Argentino’s attentions were particularly “threatening or pathological”.

In the police detention order quoted by Italian media, prosecutors said that Mr Argentino had been “regularly pestering the victim, asking her to go out with him and get to know each other better, and refusing to back down even when she would turn him down”.

Mr D’Amato said that, shortly before being stabbed, Ms Campanella sent a message to some friends, telling them that “that sick guy is following me”.

Writing on Facebook, Ms Campanella’s mother said that her daughter “bravely thought her ‘No’ would be enough because [Stefano Argentino] meant nothing to her, they weren’t together, she just wanted him to leave her alone, she wanted to live and dream and graduate.

“You always need to speak up and go to the police! Help me give Sara a voice,” she said.

In an emotional interview to Italian TV, Ms Campanella’s brother said that unrequited love or attention could never be a reason for “act like this one”.

“There are no justifications, and someone like him doesn’t even deserve words.”

The father of Giulia Cecchettin, who was also 22 when she was killed by her ex-boyfriend, told Italian newspaper La Repubblica that there are “entire generations of men who don’t accept rejection”.

“Love is not possession, jealousy is not love, and saying ‘No’ is a right. In Sara’s case there hadn’t even been a relationship,” Mr Cecchettin said.

“Women continue to be killed by those who don’t accept their rejection. We need to make an extraordinary effort, a collective act of rebellion… against this culture of death,” said Mara Carfagna, a former minister and lawmaker.

The issue of violence against women is keenly felt in Italy, where femicides are frequently reported by the media. Last month alone, four women died at the hands of their partners or ex-partners.

On Wednesday, less than 48 hours after her death, Sara Campanella’s murder was pushed out of the headlines by news that the body of 22-year-old Ilaria Sula had been found in a suitcase in Rome.

The university student had gone missing last week. According to Italian media, her ex-boyfriend has confessed to her murder.