Detectives investigating the deaths of four soldiers at the Deepcut barracks did not properly consider a list of hypothetical suspects, according to a report.
Devon and Cornwall Police reviewed Surrey Police's investigations and found the force was aware of a number of theories suggesting specific individuals could have killed the soldiers. The review found it was impossible to say whether or not the individuals should have been considered suspects or eliminated from inquiries.
But in the case of Private Cheryl James the report, which has been seen by the BBC, found Surrey Police failed to fully investigate a potential suspect known as the "unknown white male". Pte James, 18, was found dead with a single bullet wound to the head at Deepcut in November 1995.
The BBC quoted the report as saying: "The unknown male should have been subject to a Trace and Interview action. Operation Stanza (the review) believes insufficient investigative work took place to identify this unknown male who could have potentially been a suspect."
The other soldiers who died from gunshot wounds at Deepcut in controversial circumstances between 1995 and 2002 were Pte Sean Benton, 20, from Hastings, East Sussex, Pte Geoff Gray, 17, of Hackney, east London, and Pte James Collinson, 17, of Perth, Scotland.
A coroner recorded a verdict of suicide for Pte Benton but the inquests into the other three returned open verdicts.
The Devon and Cornwall review also found: "While acknowledging the large quantity of work conducted by Surrey Police with an open-minded intention, Operation Stanza has found some evidence of a possible mindset held by key individuals directing and controlling enquiries who have indicated the re-investigations were in some way 'different'."
Des James, Pte James's father, told the BBC: "It was clear to us that the investigation was about a suicide not an open-minded investigation to find out what had happened to my daughter and the other three boys."
But in a statement Surrey Police told the broadcaster the force had had "an open-minded approach" and "considered all hypotheses with equal weight". A force spokesman said: "Homicide was one of several potential hypotheses into the unexplained deaths. We believed that this investigation was different to a standard murder investigation because these were unexplained deaths.
"However, we did interview a number of people as significant witnesses to ensure that we fully examined their roles in the events that took place and we adopted and used the broad principles contained within the murder manual. Devon and Cornwall Police produced no evidence to say that we missed anything by not following this process."
