Additional reporting by the Daily Telegraph.
The man who vanished into thin air
A young man in a pink shirt, hands buried in the pockets of his fashionable white jeans, strolls jauntily through the centre of the cathedral town of Bury St Edmunds.
He stops, looks around, and decides to turn right, past a couple of hanging baskets.
Then he disappears into a cobbled loading area immediately behind a branch of the high street bakery Greggs.
It's 3.25am on Saturday, September 24, 2016, and these grainy CCTV images, circulated by Suffolk Police, show the last known movements of 23-year-old serviceman Corrie McKeague.
He was reported missing the following Monday, around 48 hours later, after failing to report for duty at his nearby airbase RAF Honington. That was almost two years ago.
Since then, McKeague's disappearance has confounded police, transfixed amateur sleuths and sparked one of the most baffling manhunts in recent memory, the Daily Mail reports.
At its centre is a single, unanswered question: how could a grown man, walking through the centre of a town equipped with numerous CCTV cameras, vanish into thin air?
Police say it's virtually impossible to walk more than a few metres from where McKeague was last seen without being caught on camera.
There was no obvious way, at that time of night, to hide from view by entering an adjacent building. And detectives can find no evidence to suggest he was taken away in a car or other vehicle.
Exhaustive searches of the Suffolk town and the surrounding countryside have failed to establish his whereabouts.
A huge PR campaign, followed by hundreds of thousands of messages on Facebook and Twitter, has led nowhere. Appeals for witnesses on radio and TV have come up blank.
A team of private investigators, employed by the family, and paid for via a crowd funding campaign that has raised tens of thousands of pounds, has been unable to elicit productive clues.
The plot thickened when it emerged that McKeague, who had been described by relatives as "happily single", was to become a father: a 21-year-old local woman called April Oliver told the BBC that she was not only his girlfriend, but was four months pregnant with his child.
So what happened to the missing RAF man? And where are the clues that might solve his disappearance?
What do we know?
A "gregarious" character who "loved to be the centre of attention", according to his mother Nicola Urquhart, the RAF Regiment gunner had arranged to spend Friday night in Bury St Edmunds with friends from his digs on the airbase. However, he missed his arranged lift.
So at 10pm, he drove to town, parking his BMW Z4 sports car in a pay-and-display carpark on Robert Boby Way, next to Waitrose. At 10.10pm, he phoned his brother Darroch. They spoke for roughly half an hour while McKeague consumed several alcoholic drinks in his car.
At 10.50pm he joined pals at the nearby So Bar, before walking to a large branch of Wetherspoon in Bury's former Corn Exchange building. At half past midnight, the party adjourned to the Flex nightclub. At the entrance, manager Ben Manning said he had asked McKeague if he was inebriated, to which the serviceman replied "yes", and said "I love you", before "stumbling" inside.
He stayed for just half an hour, before being ejected by doorman Will Hook because he had "consumed enough alcohol" and was drawing attention to himself.
McKeague agreed "amicably" to depart, says Hook, and left the nightclub, becoming separated from his friends.
His next stop was Pizza Mama Mia, a fast food joint about 450m away where he jovially played rock paper scissors with a fellow customer, before ordering two burgers, a kebab, and a portion of chips.
At 1.20am, police CCTV cameras showed him walking past the Grapes pub, en route to the doorway of an electrical store called Hughes, where he sat down to eat and subsequently fell asleep. A passer-by later prodded him to check he was okay.
About 3am, the serviceman woke up and looked at his mobile phone, a Nokia Lumia 435.
At 3.08am, he sent a text message to a friend, containing a picture of a previous night out. He then got to his feet and was filmed for the final time, walking into the area behind Greggs, at 3.25am.
Sometime later, mobile data records his phone was in the vicinity of Barton Mills, a town 20km northwest of Bury. It was moving at a speed consistent to that of a vehicle, police said at the time.
At roughly 8am, the phone stopped transmitting, suggesting it had either run out of battery, been turned off, or destroyed. It has not been recovered.
Why wasn't he seen again by CCTV?
The search initially focused on speculation that he had tried to walk the 12km back to his airbase. "He's known to go on nights out with his friends and make his way back to wherever he's based on foot," police said.
A major search and rescue operation was mounted, and teams scoured miles of rural verges amid fears that he might have either fallen into a ditch, or been thrown into one after being hit by a vehicle.
But to no avail. Once CCTV began to be fully analysed, however, it became apparent that the chances of him having wandered out of Bury undetected were extremely remote.
There are 61 police cameras in the town, along with dozens more belonging to businesses and private residents. They contain more than 1100 hours of footage of the time, which have now been closely studied by investigators.
None of them show him leaving the loading area behind Greggs, which police have described as a horseshoe, or passing along any nearby street. Some cameras are fixed, and others rotate.
They do not provide total coverage of every possible exit route for the entire time, but police say it is "highly, highly unlikely" that McKeague could have left town on foot without being filmed.
"We can't be 100 per cent sure, but we've analysed everything, from whether a person could squeeze along a wall undetected, to whether they could run down a particular street when the camera was rotated in a certain direction," police said.
"There are some gaps in coverage, but they are tiny. There's no more than a 1 or 2 per cent chance that he walked away, even if he was trying not to be seen."
Walking home would also seem a curious choice, given that he needed to return to town by 9am to prevent his BMW from getting a parking ticket. A more sensible option might have been to sleep in the vehicle.
What is more, the route to RAF Honington (where Prince Harry inspected fellow servicemen two years ago) would either take him through a series of villages, or along the verge of the busy A134 dual carriageway. Yet no witnesses report seeing him.
Could a rubbish truck have crushed him?
A week after McKeague vanished, police identified a truck emptying bins belonging to waste firm Biffa which was one of just four vehicles seen on CCTV footage around the "horseshoe" area during the hours he went missing.
The truck's route had taken it to a recycling centre near Barton Mills, at around the time the serviceman's mobile phone was in the area.
There have been several reported cases, in recent years, of intoxicated people falling asleep in rubbish bins before being crushed in trucks that come to empty them.
So it was initially feared that McKeague had had a tragic accident. However, the truck was fitted with a weighing device, which records how much waste it collects, so that clients are billed accordingly. This showed that the recycling bin it emptied outside Greggs contained less than 15kg of material. McKeague weighs around 85kg.
Detectives have checked the calibration of the device and say it is accurate. They also say it is impossible for McKeague to have hitched a ride on the vehicle without being detected.
His mobile phone was not found at the recycling centre where the lorry was unloaded. Other bins in the area were emptied several days after he went missing. They were forensically examined, but nothing was found.
A couple more bins, in a loading bay opposite the horseshoe, have not been tested. It's possible, if extremely unlikely, that he could have accessed them without being seen on CCTV.
Was he taken by Isis?
Bury is just half-an-hour's drive from RAF Marham, where two men of Middle Eastern appearance, armed with a knife, tried last July to abduct a serviceman who was jogging along a rural lane.
He escaped after knocking one of his assailants to the ground as they tried to drag him into a people carrier. The kidnap attempt took place on the same day that Isis released a video calling for attacks on Britain and other countries in the coalition bombing the terrorist group in Syria and Iraq.
About a fortnight after McKeague's disappearance, his mother said police had mentioned the possibility of a similar kidnap "and it's not something they would rule out".
Detectives said they were keeping an open mind on this front. However, as time passed, it was deemed increasingly unlikely.
First, Islamic terrorists tend to claim responsibility quickly but no group or individual has done so in this case.
Second, there was no obvious way such an attacker would have known that McKeague was in the armed forces unless he was followed from his base.
Third, and perhaps most importantly, police soon tracked down each of the three other cars in the area around the time he vanished. They have spoken to all of owners and believe there is nothing untoward in their presence.
Did he just go absent without leave?
Initially, one possibility was that McKeague had decided to do a runner from the RAF. With that idea in mind, his uncle Tony Wringe, a former serviceman, issued a message via Forces TV in early October saying: "If for any reason that you're now AWOL, it's a storm in a tea cup. We've all been there.
"We've all done dumb stuff in our service time, but in a fortnight from now this will just be a bar story. So get in touch."
Friends, however, say McKeague was happy with his job and enjoying RAF life.
His brother Darroch, who spoke to him on the night he vanished, saw no signs of unhappiness. Indeed, McKeague was planning for the future, having booked plane tickets to visit family in Scotland at Halloween.
"If you picked a happy conversation between me and him that was it," says Darroch.
More importantly, McKeague made no obvious arrangements to disappear. His pet puppy, a 7-month-old cross-breed called Louell, was left in his bedroom on the base, along with his passport.
There has been no activity on his bank or credit cards, and his email and social media accounts contain no evidence of him making any such plan.
Was he lured into a honey trap?
Fit, vivacious, confident and good-looking, McKeague had a colourful love life.
Having split from one girlfriend, an actress called Chloe Fox, in 2015, he was active on the dating websites Plenty of Fish and Tinder. Like many young men, he would regularly chat up girls in bars and nightclubs.
Did an attempted romantic advance backfire? Did he anger someone's boyfriend on the night he went missing?
Or, more sinisterly, could someone have used an online dating platform to lure him into a dangerous situation via his mobile phone?
In late November, McKeague's mother Nicola, a police liaison officer, speculated as much, saying: "Corrie was single and on dating sites. He had met girls within a short period of meeting online.
"But perhaps he was tricked into meeting someone who wasn't who they claimed?"
A further complication was the revelation that McKeague was dating April Oliver, 21, who said she s having his child.
She says they were not in an exclusive relationship, however, and he does not seem to have known she was pregnant.
Eaten by pigs, fell down a hole, abducted by aliens?
Police searched and re-searched buildings adjacent to the loading area, including a branch of Superdrug and Greggs, but to no avail.
The absence of credible evidence about his fate has duly spawned a slew of wild conspiracy theories, many of which are aired on Facebook.
These have ranged from the unlikely suggestion that he trie to walk home, but wandered onto one of the many free-range pig farms on the way and was eaten by the animals, to speculation that he somehow engineered his own disappearance by vanishing down a storm drain and sneaking out of the centre of town via a sewer.
Others wonder if he accidentally stumbled upon a drug deal, or somehow managed to evade detection by CCTV cameras by drunkenly crawling out of the centre of town (and then jumping into a car that offered him a lift).
His mobile phone's apparent appearance 20km away has sparked several theories involving a robbery, and road works in town has also prompted speculation that he fell into a hole in the road and disappeared.
Then there are inevitable contributions by supposed clairvoyants, along with comments by individuals who believe in the possibility of alien abduction. Over the next two years, the sense of mystery about this perplexing case seems to deepen.
Two years later
The inquiry into the disappearance of RAF gunner Corrie McKeague will be stood down this year and passed to a cold case team, police have confirmed, as the airman's father said he fears he might have killed himself.
Suffolk police say investigators had been through all realistic possibilities in detail and that there was no evidence of foul play.
McKeague's father Martin told the Daily Mirror he fears the airman might have killed himself.
The 49-year-old said he thought his son knew he was going to become a father, which might have affected his mental state.
He said: "I just can't help thinking this would have weighed on him heavily and he may have actually chosen to get in that bin that night knowing what would happen.
"It's as probable as anything else and it makes it no less heartbreaking."
Detective Superintendent Katie Elliott said: "It is extremely disappointing that we have not been able to find Corrie. I can only imagine the strain Corrie's family have been under over the past 18 months and I thank them for their patience and understanding.
"While the investigation has drawn to a natural conclusion we will continue to work with the family to provide answers to their questions and help them understand what may have happened.
"Since Corrie disappeared, police have been exploring all proportionate and relevant lines of enquiry.
"We have now reached a point where we are unable to make any further progress, and have gone as far as we realistically can with the information we have. If any new, credible and proportionate enquiries relating to Corrie's disappearance emerge we will pursue them."
Assistant Chief Constable Simon Megicks said the inquiry had been reviewed by senior officers as well as external experts, and he had "absolute confidence in the way the investigation was conducted".
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