Raffaele Sollecito maintained he believes Amanda Knox didn't kill British student Meredith Kercher, although his lawyers are seeking to distance him from his co-defendant and ex-lover as part of a new defence strategy.

Sollecito's lawyer Giulia Bongiorno told a press conference in Rome that Knox lied to her client about key evidence in the case, proving that the two were not together minutes before Kercher was killed.

Kercher, from Croydon, south London, was found with her throat slashed inside the apartment she shared with Knox in the university town of Perugia, central Italy, on 1 November 2007.

Bongiorno said that Knox and Sollecito spent that night together at his home, but were apart earlier in the evening.

"Raffaele has always maintained he spent the night with Amanda, but during the first part of the evening they were not together," Bongiorno said.

According to Italian authorities Kercher was killed sometime between 9 and 9.30 pm.

Part of Knox's alibi was based on an SMS she claimed to have sent from Sollecito's house to Patrick Lumumba, the owner of a bar where she worked, at 8.35 pm.

Bongiorno said the claim was proved to be a "lie" during the trial, as evidence showed she was nowhere near her lover's flat when text was sent.

According to the sentence that found the pair guilty over the murder in January, the SMS was received by a mobile phone network base station that covered a different area from that including Sollectio's house, Bongiorno explained.

The lawyer said she believes both Sollecito and Knox are not guilty, but urged judges to consider the two as separate entities.

"They are not Siamese twins - one body with two heads," she said.

The plea came as Sollecito's defence team is preparing to lodge an appeal with Italy's top court and marked a dramatic change of defence strategy.

Knox and Sollecito's defence teams have long maintained the pair should be tried and proved innocent together.

Sollecito's memoir book is titled Honour Bound in a reference to his relation with Knox and he has even claimed he resisted attempts by Italian police to pressure him into incriminating his ex-girlfriend.

"We believe that Amanda and Raffaele have nothing to do with it [the murder]," Bongiorno said.

"However we have also to take into consideration a second possibility ... if there are too many anomalies regarding Amanda, [judges] should not automatically extend them to Raffaele."

Nevertheless Sollecito said he is sure Knox is innocent.

"My family and I have always believed Amana is innocent. I'm not backtracking on that," he said.

Prosecutors say Kercher was killed by Knox, Sollecito and Rudy Guede, a drifter from the Ivory Coast,after an argument .

After a series of appeals and opposite rulings, Knox and Sollecito were found guilty of murder and sentenced to 28 and-a-half and 26 years in jail by a Florence appellate court in January.

They are both to lodge another appeal at Italy's Court of Cassation in Rome, which is expected to hear the case in early 2015.

Guede was sentenced to 16 years at the end of a separate trial and is serving his sentence in Viterbo jail, near Rome.