Knox, who spent four years in jail for the murder of her flatmate Meredith Kercher before her conviction was annulled, is facing a retrial for falsely accusing Patrick Lumumba, a Congolese bar owner, of the crime.
"The police threatened me with 30 years in prison, an officer slapped me three times saying 'Remember, remember'," Knox told the court, saying that police wanted her to blame Lumumba.
"I'm very sorry that I wasn't strong enough to withstand the pressure from the police," she added, speaking in Italian.
Italy's top court in 2015 annulled Knox's conviction for the murder in the city of Perugia, capping nearly a decade of courtroom drama during which she had twice been found guilty.
The brutal stabbing of 21-year-old Kercher and multiple trials provided fodder for tabloids on both sides of the Atlantic and inspired books and films.
Knox was also given a three-year sentence for wrongly accusing Lumumba of killing Kercher. The sentence had no practical impact as it was covered by the time Knox spent in jail.
The European Court of Human Rights ruled in 2019 that there had been procedural errors during Knox's questioning and Italy's highest court last year ordered a retrial in the slander case.
Lumumba was held for two weeks in 2007 before he was freed.
"When Patrick was accused by Amanda, he became known everywhere as the monster of Perugia," Lumumba's lawyer Carlo Pacelli told reporters on Wednesday, saying that the conviction should be upheld. Lumumba was not in court.
Holding hands with her husband Christopher Robinson, Knox, 36, earlier made no comment to journalists and camera crews when she arrived at the court. A verdict was expected later oon Wednesday.
Rudy Guede, originally from the Ivory Coast, was sentenced to 16 years in jail for the killing of Kercher, in a ruling that said he acted with unnamed other culprits. He was granted early release in 2021.
