Amanda Knox, an American who was convicted and then exonerated of murdering her housemate while they were studying in Italy, on Wednesday lost another trial in an Italian court against slander charges related to the 2007 killing.

Ms. Knox was convicted by a court in Florence on charges that she had slandered a man who ran a bar where she worked by unjustly accusing him of killing her housemate, the 21-year-old Meredith Kercher, in 2007. Ms. Knox was sentenced by the court to three years in prison, time she has already served.

Ms. Knox was initially found guilty of slandering the man, Diya Lumumba, also known as Patrick, in 2009, a conviction that was upheld by various Italian courts. At the time of the killing, Mr. Lumumba ran a bar called Le Chic where Ms. Knox worked part time.

Speaking to a courtroom packed with journalists before the ruling on Wednesday, Ms. Knox, referring to her comments about Mr. Lumumba in 2007, described “the worst night of my life,” and said that she had been bullied by the police into accusing an innocent man of murder.

“I was a 20-year-old who had been tricked and was psychologically destabilized,” Ms. Knox told the court in Italian, her voice cracking at times. She said she couldn’t understand why the police, “who I had been raised to trust,” were pressuring her to admit to something that was not true and to sign a document that was little more “than a mix of incoherent memories.”

The hearing on Wednesday is the latest turn in a legal journey whose echoes continue to reverberate nearly 17 years after the murder of Ms. Kercher, a British student, elicited headlines around the world and turned Ms. Knox into a tabloid staple.