Police did not take clothing samples from two soldiers at Deepcut barracks on the night a 17-year-old recruit was found shot dead, an inquest has heard.
Pte James Collinson died from a single gunshot wound
Det Ch Insp Simon Humphreys said Pte James Collinson, of Perth, apparently said he would shoot himself in 2002.
He said other soldiers were dealt with as witnesses not suspects because facts indicated Pte Collinson was on his own.
The hearing follows inquests into the deaths of three other Deepcut soldiers, from Sussex, Wales and County Durham.
The inquest at Epsom Magistrates' Court heard Surrey Police had been called to the barracks on 23 March after Pte Collinson was found dead.
He was on duty with Pte John Donnelly and Pte Stacy McGrath that night. They have denied any involvement in his death.
Mr Humphreys said police were told he had apparently expressed the intention of shooting himself, had borrowed a rifle, and walked off on his own before a shot was heard and he was found dead.
Mr Humphreys said that later he found out another recruit, Pte Geoff Gray, of Seaham, County Durham, had died six months beforehand. Pte Gray's inquest was held in the week leading up to Pte Collinson's death.
The police officer said the force then put out a statement saying "further investigations" into Pte Collinson's death were under way.
Clockwise from top left: Sean Benton, James Collinson, Geoff Gray and Cheryl James
The inquest also heard a routine post-mortem examination was ordered with the condition a "special" post-mortem be carried out if suspicious signs were found.
Mr Humphreys agreed when Surrey coroner Michael Burgess asked him: "Is it right that early on the opportunity to check material from others, for example the two on guard duty with him, was lost?"
Mr Burgess asked if that was because of Mr Humphreys' decision, and the officer replied: "That was based on a hypothesis that I had formulated on the evidence that I had."
The hearing heard the inquiry was later widened to include the deaths of three other Deepcut recruits: Pte Sean Benton, from Hastings, Pte Cheryl James, from Llangollen, and Pte Geoff Gray, from Seaham.
Det Supt Brian Boxall, who led a combined investigation into the deaths at Deepcut, told the hearing a major search of the area where Pte Collinson's body was found was carried out eight months after the death.
He said the Collinson family lost confidence in the Surrey Police investigation and that the force had since dropped its method of investigating crimes based on a hypothesis.
Mr Boxall said: "I think it was recognised through the response by the family that that probably wasn't the best way of dealing with it.
"One of the things we have learned from the investigation is that it is always important to get the confidence of the family as it is to satisfy ourselves, because it is their loved one that has died."
The hearing will continue on Wednesday.