Jeremy Bamber in new challenge to conviction for murdering family Jeremy Bamber in 1986. He has always denied killing five members of his family at their Essex farmhouse. Photograph: Trinity Mirror/Mirrorpix/Alamy Jeremy Bamber, who was jailed for 26 years for killing five members of his own family, is launching another bid for freedom after evidence emerged that the assistant director of public prosecutions decided not to proceed with drug trafficking and fraud allegations against a key prosecution witness. His legal team is expected to argue that this raises the possibility that she was induced to give evidence against Bamber in return for the allegations being abandoned. Bamber, now 51, was found guilty in October 1986 of shooting his adoptive parents, June and Nevill, his sister Sheila Caffell and her six-year-old twins, Daniel and Nicholas, at their Essex farmhouse. He has always maintained his innocence. Julie Mugford, who gave evidence against her ex-boyfriend Jeremy Bamber. Photograph: PA Archive/Press Association The prosecution witness Julie Mugford was Bamber's girlfriend in the runup to the killings. After their relationship broke down following the murders, Mugford told police Bamber had confessed to hiring a hitman to kill his family. That theory collapsed when the man named was found to have a cast-iron alibi, but Mugford's evidence was crucial to the prosecution's case. The trial judge told the jury they could convict Bamber on her evidence alone. Now Bamber's lawyers have discovered Mugford testified against him after police decided to drop investigations into criminal offences she had allegedly committed before the trial. Documents only recently disclosed to Bamber detail how Mugford was accused of burglary, smuggling cannabis into the UK from Canada and cheque fraud. The Guardian has seen a letter from the then assistant director of public prosecutions (DPP), John Walker, to the chief constable of Essex, which stated: "With considerable hesitation I would suggest that Mugford be advised she will not be prosecuted in respect of these matters - burglary, cheque fraud and cannabis offences. Thereafter she will be called as a witness against Bamber. Further documents relating to the dealings between the DPP and Mugford remain undisclosed under public interest immunity rules. Bamber's lawyers have sent the new evidence to the Criminal Cases Review Commission (CCRC) in an attempt to get his case back to the court of appeal for a third time. The claims are examined in a documentary on ITV on Thursday at 7.30pm. Bamber's lawyers have also asked the CCRC to consider evidence from eminent ballistic experts indicating the family were killed by a rifle without a silencer attached to the barrel. The silencer was crucial to the prosecution case against Bamber. It was found days after the killings and the Crown's case was that Caffell, who police initially believed had killed her family before shooting herself, could not have done so and then removed the silencer from the gun.