Police searching for missing airman Corrie Mckeague say they are “confident” his body will be found at a landfill site.
The RAF serviceman has not been seen since a night out in Bury St Edmunds, Suffolk, in September.
Suffolk Police revealed a bin lorry seized shortly after the gunner vanished was carrying a heavier load than first thought.
The force is now searching a landfill site in Cambridgeshire as a result.
Det Supt Katie Elliott told the BBC: “I have a strong belief that we will find him here.”
Asked for her reaction to the delay in the correct information about the weight of the lorry’s load coming to light, she replied: “It’s frustrating for me, I think it must be terribly frustrating for Corrie’s family.”
Det Supt Elliott said she would “have liked to have had the information sooner that would have led us to this point”.
She said finding out about the lorry weight mistake was “very sobering”.
“We’ve been working tirelessly on this investigation to try and find Corrie – that’s been our priority the whole way through.
“To have that information really reinforced the decision that we’d already made that we needed to come and search this landfill site.”
Mr Mckeague was last seen on CCTV cameras walking into a loading bay area of Bury St Edmunds known as the “Horseshoe”.
After he was reported missing, signals showed his mobile phone had been in nearby Barton Mills, and matched the route of a bin lorry.
Police were initially told the waste collected from the area weighed 11kg (1st 10lb), too light to have contained Mr Mckeague.
The force has since found out the lorry’s load was more than 100kg (15st 10lb).
A search team at the landfill site in Milton, Cambridgeshire – where the lorry’s load ended up – has already trawled through 60 tonnes of waste.
It could take the team of eight trained officers up to 10 weeks to sift through the rubbish, which covers an area of about 920 sq m (9,900 sq ft).
Asked if Mr Mckeague’s family had wanted police to come to search the site sooner, Det Supt Elliott replied: “We had discussions with the family around coming to search the landfill site at the beginning of the investigation when we understood Corrie’s phone [was] tracked at a similar pace to the waste lorry.
“However, the information at that point did not lead us to believe that it was justifiable to come and search here. The strongest line of inquiry at that time was that Corrie had tried to walk home.”