A bin was mistakenly thought to have been too light to have had missing RAF gunner Corrie McKeague inside it because of a miscalibrated weighing device, an inquest has heard.
Mr McKeague, who was based at RAF Honington, was 23 when he disappeared in the early hours of September 24, 2016, after a night out in Bury St Edmunds.
He was last seen on CCTV at 3.25am on September 24 entering a service area behind a Greggs store in the west Suffolk town centre, but his remains have never been found.
Police believe the serviceman had climbed into a bin, which was then tipped into a waste lorry.
Waste firm Biffa initially told police that the weight of the bin was 11kg (1 stone 10lbs) but it was later recorded as 116kg (18 stone 3lbs).
Stephen Graham, IT services director for Biffa, told an inquest at Suffolk Coroners' Court in Ipswich how weights are recorded.
He said: "Truck goes out, picks up bin. When you weigh a bin the bin is weighed twice.
"Once when it goes up, once when it comes down, and weight is generated be the difference. Full, empty, one minus two."
He said that, after a bin has been emptied, the driver pushes a button to get the weight on a device in the bin lorry.
These are later uploaded from the device to Biffa’s database.
Asked about other weights displayed in the database beside the Greggs bin other than the reported 116kg, including the initially reported weight of 11kg, Mr Graham said: "From our investigations, during the course of this inquiry we’re able to see these are bins that were previously collected and we believe they came from the depot where the lorry was kept.
"They are unfortunately confirmed against the Greggs single bin pick up."
He said that there was "no contract to accept (the bins from the Biffa yard) against" so they were confirmed against the Greggs bin.
He continued: "It’s an error in the process as the device hasn’t been cleared after picking up bins at the Biffa depot.”
Mr Graham said a timestamp by the 116kg weight showed it was from September 24, and timestamps by the other weights, including the 11kg, showed they were from September 23.
He said at the time it had mistakenly been thought that the most recent weight lifted would be at the bottom of the list on the database, but actually it was at the top.
He said he was "99% confident” the 116kg reading was "correct", adding "perhaps I should have said 100% – I think there’s always 1% somewhere for room for anomaly in the world of computers but otherwise 100%".
Bin lorry driver Martyn Thompson previously told the inquest that he lifted the lid of the bin when he collected it at 4.19am on September 24 and there was no-one inside.
Asked if he could explain the difference between the 116kg weight and what the driver said he saw, Mr Graham said: "Personally no. All I can say is this is what the weighing equipment says and this is what the system says.
"I can’t account for what the driver saw."
The inquest, being heard before a jury, continues.
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