An investigator has outlined four theories police considered as they probed missing airman Corrie McKeague's disappearance.
Chief Superintendent Marina Ericson, who became senior investigating officer on the case in 2017, shared the details as she gave evidence to an inquest on Monday.
Mr McKeague, 23, was last seen in the early hours of September 24, 2016 after a night out in Bury St Edmonds.
The gunner, who was based at RAF Honington in Suffolk, had previously slept inside a bin and was a heavy sleeper when drunk, the inquest was told.
He was captured on CCTV at 3.25am entering a service area behind a Greggs store.
Police believe he climbed into a bin, which was then tipped into a waste lorry.
Spt Ericson, who became senior investigating officer on the case in 2017, told the inquest Mr McKeague was reported missing by senior officers at RAF Honington at 3.42pm on Monday September 26.
The airman's disappearance was treated as a "high risk" case as he was in the RAF, she added.
Spt Ericson said the disappearance was out of character, and at the time the major investigation team was also investigating reports of an attempted kidnap at RAF Marham in Norfolk in July 2016, which "was later discounted".
She described four overarching hypotheses concerning how Mr McKeague had disappeared to the inquest.
Detectives' four possible theories for Corrie McKeague's disappearance:
That Mr McKeague died following an accident.
That he died as a result of criminality.
That he remains alive but held against his will and unable to contact anyone.
Or, that he remains alive and is deliberately staying away and does not wish to be found.
Spt Ericson told the inquest one line of inquiry centred on looking at Mr McKeague's lifestyle.
She agreed with Peter Taheri, counsel to the inquest, that she said in a witness statement that "Corrie stated to a colleague he had previously slept in a bin".
Asked for the source of this information, she said: "Two witnesses who were colleagues of Corrie McKeague."
The superintendent said in her witness statement that Mr McKeague "was described as being a heavy sleeper when drunk".
Asked by Mr Taheri for the source of this, she responded: "Colleagues, friends, I believe some of the family statements made reference to how he slept when he had had a drink."
Spt Ericson also said that the movement of the airman's mobile phone appeared to match the movement of a bin lorry that collected a bin from the service area where Mr McKeague was last seen.
She said that a hypothesis that Mr McKeague climbed out of a horseshoe-shaped area in Brentgovel Street was "thoroughly investigated" and found to be unlikely.
"We talk about the scale and nature of the buildings, the angle and slope, pigeon spikes and netting, the drain pipes being set into the buildings so you don't have the grip behind the drain pipe itself."
Spt Ericson also told the inquest that Mr McKeague was not seen by witnesses or on CCTV after entering the service area, and that he was "believed to be significantly under the influence of alcohol and from CCTV footage he can be seen to be unsteady on his feet, which would have hindered any attempt to climb the buildings surrounding this area."
She added that 1,843 witnesses were spoken to during the investigation, with two people treated temporarily as suspects before both were told they would face no further action.
Andrew Graves, a product marketing manager for waste vehicle manufacturing firm Dennis Eagle, said the chances of someone surviving inside the back of a bin lorry were "slim".
"The chance of survival is slim, but if anything suffocation is likely to be the most likely cause of death if the person isn't immediately crushed," he said.
Mr Graves said that 30 tonnes of force is exerted during each compaction cycle in the back of a bin lorry, each lasting 18 to 20 seconds. If someone survived until the lorry reached a waste transfer station, they would have to "keep above the waste" as it was being tipped out, he said.
He said there was 10.8 tonnes of waste in the bin lorry in question, and that it comes out "like an Oxo cube".
Pressed to give a percentage chance of survival, Mr Graves said: "I give a 5% chance of survival."
The inquest, being heard with a jury, continues.