A juror who helped to convict Amanda Knox has revealed she has 'grave doubts' over the American's involvement in the murder of Meredith Kercher. Knox is pictured above in Seattle last month . A juror who helped to convict Amanda Knox has revealed she has 'grave doubts' over the American's involvement in the murder of Meredith Kercher. Job centre worker Genny Ballerini, who served on a panel of citizen judges that reinstated Knox's murder conviction last year, has slammed the prosecution's case citing 'questionable proof, flimsy evidence and bizarre testimony'. The motive put forward by prosecutors that Knox killed Miss Kercher after she complained about the American leaving the bathroom dirty seemed like 'nonsense', she said. Miss Ballerini, 48, suggested that the pair did not get a fair trial because there was 'an atmosphere of guilt' in the deliberation room before it even began. Miss Kercher, 21, from Coulsdon, south London, was found half-naked with her throat slit in 2007 in the Perugia cottage she shared with Knox, 19. Knox and former boyfriend Raffaelle Sollecito served four years for the brutal killing but were freed on appeal in 2011. Knox immediately returned to the US and has rebuilt her life, finding love with old school friend Colin Sutherland and working on her local newspaper in Seattle. But last year an appeal court reinstated the original convictions ordering the pair to serve 28 and 25 years respectively. A third suspect Rudy Guede was convicted in a fast track trial and is serving 16 years for the murder. Italy's highest court will hear Knox and Sollecito's final appeal next week. If convicted Italy can request Knox's extradition. But while the Supreme Court could rubber stamp the conviction later this month, Miss Ballerini's claims could derail the case. The court can send the case back back to an earlier appeal stage if the decision taken by the lower court was found to be illogical or inconsistent. The juror told Oggi magazine: 'I certainly had many doubts about the guilt of the two young people. I was not convinced of their innocence but I thought and I said to the others as well: "The evidence that we have is not sufficient to inflict all these years in prison". Meredith Kercher (left), 21, was found half-naked with her throat slit in 2007 in the Perugia cottage she shared with Knox, 19. Knox and former boyfriend Raffaelle Sollecito (right) served four years for the brutal killing but were freed on appeal in 2011 . Miss Ballerini was part of the panel that reinstated Knox's conviction last year. She said: 'I said immediately that I did not agree and they took note.' Above, Knox sits alone before being interviewed in January 2014 . She added: 'There was not enough, in my opinion, to justify such a heavy sentence: questionable proof, bizarre testimony and flimsy evidence.' She dismissed the alleged motive as 'nonsense' and said: 'You do not massacre a girl because she complained about a bit of a stink in the bathroom.' And she was equally doubtful about Sollecito's motivation. 'What could possibly have been the motive that Raffaelle had to participate in the killing of that poor girl.' When she heard the verdict and sentence she immediately protested. Miss Ballerini said: 'I said immediately that I did not agree and they took note. Other members of the jury were also against an increase in the sentence, she said, but they were told there was no alternative.' The jurors constructed a timeline with mobile phone records and statements from the witnesses that showed how the pair could have been at the murder scene at the time of death, but she questioned whether it was sufficient proof to condemn them. She was equally unconvinced by attempts to portray the pair as bad characters. Prosecutors had painted Amanda as troublesome because she once received a fine from police for being disorderly. 'This seemed to me, excuse me, more nonsense,' she told the weekly magazine. Knox (above with police) reacts after hearing the verdict during her appeal trial in Perugia on October 3, 2011 . Miss Ballerini added that 'there was not enough [evidence], in my opinion, to justify such a heavy sentence'. The couple are pictured above kissing after Miss Kercher's body was discovered . Sollecito was described in the initial trial as 'depraved', because he read violent Manga comics, but Miss Ballerini said reading comics or watching cartoons did not amount to being a killer. 'If someone is a murderer you have to prove it,' she said. Crucially the only person definitively convicted of the murder had not implicated the pair. He has given three different accounts of the murder and never said that Knox and Sollecito were with him, she pointed out. Continuing to pick apart the case she said it was strange that Knox and Sollecito had barely left a trace of DNA in the room where Meredith's body was found whereas Rudy Guede left 'a good number' of marks. 'They claimed that Knox had removed her traces by cleaning. Pah! Today when I think about it again I have even more doubts,' she said. But she insisted that the two professional judges on the panel had not tried to sway the jury. She claimed that she herself had not had an opinion because she had not read about the case in the news but had developed her convictions studying the files on the previous trials and keeping a diary where she recorded what happened at every hearing.
Genny Ballerini served on panel that reinstated Knox's conviction last year . 48-year-old suggests American and Raffaelle Sollecito did not get fair trial . Motive was 'nonsense' and proof was 'questionable', Miss Ballerini said . Knox and Sollecito served four years but were freed on appeal in 2011 . Last year an appeal court reinstated their original murder convictions .