Perugia , Italy ( CNN ) -- Amanda Knox , the American student convicted of killing her British roommate Meredith Kercher in Italy , faced a surprise accusation Monday from another man behind bars for the murder . Rudy Guede refused to say Knox was not involved -- and prosecutor Giuliano Mignini read out a letter saying Guede thought the American and her then-boyfriend had killed Kercher . Guede wrote to a news website in the spring of 2010 , after the three were convicted , referring to `` a horrible homicide of a splendid young girl , Meredith Kercher , by Amanda Knox and Raffaele Sollecito . '' Mignini produced a copy of the letter on Monday during Knox 's appeal against her conviction . Defense lawyers said they did not know of the existence of the letter before Mignini read it in court . Knox took the stand for emotional testimony after Guede spoke , saying she was `` shocked . '' `` The only time that Rudy Guede , Raffaele Sollecito and I were in one room together was in a court room ... . He knows what the truth is . I do n't know what happened that night , '' she said . Monday 's appeal hearing was the first time the three people convicted of the crime appeared in court together since a preliminary hearing years ago . Kercher was found stabbed to death in 2007 at the house she shared with Knox in Perugia , the central Italian town where both were students . She was semi-naked and her throat had been slashed . Knox , 23 , and her then-boyfriend Sollecito , 27 , were convicted of the murder in 2009 . Guede was found guilty in a separate fast-track trial and sentenced to 16 years . Defense lawyer Carlo della Vedova and Knox 's mother Edda Mellas both rejected Guede 's testimony Monday . Her father Curt Knox , speaking to CNN from Seattle , said it was `` very disappointing that he will not own up to his responsibility . '' Under cross-examination , Guede said he had written what he always believed , but that it `` was not up to me to say who was the killer . '' Della Vedova said Guede 's letter was based on `` a feeling '' and that his accusations are not based on facts or events he witnessed . Mellas said Guede `` continues to lie about Amanda and that 's unfortunate . '' `` He did n't say much . He refused to answer most of the important things , '' she said . `` Amanda wanted to be able to confront him and she was denied that . '' Mellas said she had suffered watching her daughter testify : `` It 's devastating to watch your child in pain . It 's horrible to see her go through that . '' She said before the hearing she can not understand why Guede might spend only seven years behind bars if he is released early for good conduct , while Knox could serve 26 years . Sollecito said Monday he and Knox had been behind bars for nearly four years , their lives destroyed based only on suppositions . Francesco Maresca , the lawyer for the Kercher family , said Guede 's testimony was the first time he has said `` clearly that the two defendants were present in the scene of the crime that night . '' The hearing is now adjourned until July 25 , with further hearings on July 30 and August 1 . The appeal hearing has heard a confusing array of stories from a range of convicted criminals this month . Guede had been called as a witness to corroborate the story of another convict who told the court just over a week ago that Guede had said Knox and Sollecito were not involved . But on the stand , he did not back Mario Alessi 's version of events . As part of the 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 . An independent forensics study on the DNA evidence is due Thursday , Curt Knox said Monday . `` We 're hopefully going to hear good news that it 's incompatibale to Amanda and not useful , '' Knox said . 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 . CNN 's Hada Messia and Dan Rivers contributed to this report .
NEW : Knox hopes DNA report due Thursday will help her defense , her father says . Amanda Knox says she is `` shocked '' by the testimony of Rudy Guede . Guede , convicted separately of killing Meredith Kercher , denies another convict 's story . Knox and her former boyfriend were found guilty in 2009 of killing Kercher in Perugia .