Rome (CNN) -- Two inmates testified Saturday that Amanda Knox, the American student convicted of murder in Italy, was not actually involved in the killing of her roommate. But they offered two different accounts on who the actual killers were.

Three other inmates testified as well.

Knox was sentenced last year to 26 years in prison for the death of Meredith Kercher at a house the two shared in Perugia, the central Italian town where both were students.

Knox has vehemently proclaimed her innocence and her family has continued to fight the conviction.

Two hours of legal wrangling between attorneys passed before the judge decided to allow inmates Mario Alessi and Luciano Aviello to testify. Alessi is serving a life sentence for kidnapping and killing an 18-month-old boy.

Alessi testified that Rudy Guede, who has also been convicted in Kercher's murder and is serving a 16-year sentence, told him that neither Knox nor her Italian boyfriend at the time, Raffaele Sollecito, were involved in the killing.

Later in the day, Aviello, who has ties to the Naples Mafia, testified that it was his brother who was the killer, together with an Albanian man.

According to Alessi, Guede said that he and an unnamed friend visited Kercher to try to get her to participate in sexual acts. When Kercher denied them, Guede's friend forced himself on her, and Guede also participated, Alessi said. At one point, the friend pulled out a knife, and then Guede, who was holding Kercher at the time, noticed she had started bleeding, Alessi testified.

Alessi told the court that Guede tried to stop the bleeding, but that his friend urged him to leave.

"We need to finish her otherwise she will tell on us," Alessi quoted the friend as telling Guede. The friend then proceeded to inflict another wound on her, Alessi testified.

Alessi said Guede remained by himself with Kercher for a while, but eventually left her injured.

Prosecutors and the lawyer for Kercher's family questioned the validity of Alessi's testimony.

Through his lawyers, Guede denied Alessi's version of events.

During his testimony, Aviello gave a different account.

Aviello said that on the night of the killing, his brother came home with scratches and other wounds. As Aviello tended to the wounds, his brother confessed to him that he had killed Kercher, he said.

According to Aviello, his brother said that he and an Albanian man entered the residence to steal a painting, and in the act ended up killing the girl. Aviello said he hasn't seen his brother in three years.

"Inside me I know that a miscarriage of justice has taken place," Aviello said of Knox and Sollecito's conviction.

Prosecutors questioned his credibility and Aviello admitted that he has been convicted of defamation seven times.

The appeals process will continue June 27, when Guede is expected to testify.

In an additional twist Saturday, another inmate who the defense put on the stand to verify Alessi's version of events, testified that he, in fact, did not know anything about who carried out the killings. Even though his cell was adjacent to Alessi's and Guede's, the inmate was Romanian and didn't know what they discussed, he said.

Another witness Saturday was Marco Castelluccio, a Mafia member who testified from behind a screen because he is a protected witness.

Castelluccio said that he also heard from Guede that Knox had nothing to do with the crime.

Kercher, 21, was found dead on November 2, 2007, seminaked with her throat slashed. Knox and Sollecito were both found guilty of the murder. Knox was sentenced in December 2009.

Guede, a drifter originally from Ivory Coast, was tried separately.

As part of her appeal, forensic experts are retesting evidence that was used to convict Knox.

That evidence includes a knife found in Sollecito's apartment with Knox's DNA on the handle and what Perugia prosecutors say is Kercher's DNA in a tiny groove on the blade.

The prosecution contends that the knife was used to stab Kercher in the neck and that it had been cleaned. The DNA matter attributed to Kercher consists of flesh, not blood, they say.

The sample, however, was so small that forensic scientists investigating Kercher's murder were not able to double-test it in accordance with international forensic science norms, which Knox's legal team says raises doubts about its validity.

The second piece of evidence the forensic experts are testing is the tiny metal clasp from Kercher's bra, which was cut from her body after her slaying. Forensic scientists in the investigatory phase determined that Sollecito's DNA is present on the metal clasp.

The clasp was identified on an investigatory video the same day Kercher's body was found. But it was not collected until nearly six weeks later, giving the defense cause to question whether the sample may have been contaminated.