Whether it’s one-off unexplained incidents, long-running riddles or conspiracy theories, unexplained mysteries have long captured the public’s imagination.
Here are six of the biggest unsolved sagas which captivated Britons in 2017.
The ‘Putney Bridge Pusher’
Putney Bridge became the unlikely focus of media attention in August.
Shocking CCTV from south-west London showed a male jogger pushing a woman in front of an oncoming bus, which had to violently swerve.
The incident, which took place on 5 May, months before the public appeal for information, could have ended in tragedy were it not for quick-thinking bus driver Oliver Salbris.
Following the appeal, police arrested a 41-year-old banker over the incident – before he promptly proved that he was nowhere near London at the time of the incident.
Months later and despite numerous appeals, no one knows the identity of the jogger, or why he pushed his 33-year-old victim.
The M25 cat killer
Initially known as the ‘Croydon cat killer’, the unknown figure, who is feared to have killed and mutilated more than 250 cats in the past two years, remains at large.
Police began to investigate a series of killings in December 2015 under the name ‘Operation Takahe’ and within a couple of months, officers had linked the deaths of 10 cats in the south London area.
Since then, the number of deaths has continued to take place sporadically.
YAHOO UK’S YEAR IN REVIEW 2017
From Trump to Brexit via Love Island: The 20 most searched terms on Yahoo UK in 2017
Year in Review: The celebrities we lost in the last 12 months
The most popular movies of 2017 revealed
The most memorable politicians and biggest political searches of 2017
While the vast proportion of attacks have been in London, cats further afield – in Coventry and Bristol, for example – are also thought to have been mutilated by the same individual.
One of the key elements linking the killings is that the killer often removes the head or tail, which he then keeps – seemingly as a trophy.
There is also thought to be a possible sexual element to the killings, with the cats sometimes left spread-eagled below the bedroom windows of their owners.
In August, animal charity SNARL (South Norwood Animal Rescue Liberty) and Surrey Police released possible details of the killer in August.
He was described as a white male in his 40s with short brown hair, possible facial scarring resulting from acne, and dressed in dark clothing.
The disappearance of Madeleine has captivated the British public for over a decade.
Since going missing from a holiday apartment in Portugal on May 3 2007, there has been a worldwide search for the daughter of Kate and Gerry McCann.
In September 2017, the Home Office sparked renewed hope that she could be found by giving Scotland Yard an additional £154,000 to continue Operation Grange, the British investigation into Madeleine’s disappearance which began in 2011.
In recent weeks, detectives have travelled to Bulgaria to interview a waitress who was working at the resort at the time of the disappearance.
The initial Portuguese investigation closed in 2008.
Officers have until March 2018 to find significant new information, or the operation may come to an end, with Madeleine’s mystery still unsolved.
Just like the still-missing MH370, disappearing aeroplanes have long captured the public’s imagination.
More than 70 years after the world-famous aviation pioneer Amelia Earhart vanished over the Pacific, new theories continue to emerge over her sudden and unexplained disappearance.
In 1937, Earhart, who had already become the first solo female pilot to fly across the Atlantic Ocean, embarked upon her latest challenge – a circumnavigational flight of the globe.
Along with co-navigator Fred Noonan, they took off on 2 July. A few hours later, she sent her final radio message over the central Pacific Ocean near Howland Island and was never heard of again.
There are many theories over what really happened: one states that the flight crashed and sank; another that Earhart changed route; a third was that she was a spy working for the US administration and she was captured by the Japanese.
In July, the History Channel aired a documentary claiming that they had uncovered a ‘bombshell’ photo that provided evidence Earhart and Noonan crash landed near the Marshall Islands and were taken captive by the Japanese.
The image was quickly debunked after two bloggers found evidence that the same image was found in a book with a 1935 date stamp attached to it.
That said, controversy remains surrounding her disappearance – will we ever know the truth?
The Moors Murderers’ final victim
Few killers are more reviled by the British public than Ian Brady.
The child-killer died in May, and his ashes were disposed of at sea in October.
Brady, and his accomplice Myra Hindley, tortured and murdered five children in the 1960s and sexually assaulted four of them. They were jailed in 1966.
The victims’ ages ranged from 10 to 17 years old.
Four of the victims were buried on Saddleworth Moor, but the body of Keith Bennett, who was 12 when he was killed, is yet to be found.
Brady tormented Keith’s family for years, hinting that he may release details of where the body could be found. In 2012, Keith’s mother, Winnie Johnson, died without knowing where her son was buried.
Dr Alan Keightley, who claims he frequently met Brady during his time in prison and has an insight into the killer’s mind, said in May he knew where the body is buried.
But the final resting place of Keith remains unsolved and, with Brady now dead, it is unlikely the body will ever be found.
Did Russia hack the US election?
Russia’s alleged involvement with the 2016 US election grew in prominence in July 2016, when former-president Barack Obama ordered US intelligence agencies to assess whether or not Russia had played a role in a cyber attack.
The Central Intelligence Agency, the Federal Bureau of Investigation and the National Security Agency all concluded Russian president, Vladimir Putin, had ordered a campaign to not only undermine confidence but also to affect the election outcome.
President Trump’s former campaign manager Paul Manafort was indicted in October after pleading guilty to lying about his interactions with foreign officials close to the Russian government.
George Papadopoulos, Trump’s former foreign policy advisor, was also found to have lied ‘about the timing, extent and nature of his relationships and interactions with certain foreign nationals whom he understood to have close connections with senior Russian government officials,’ according to the complaint.
Trump firmly believes the Russia investigation should come to an end. ‘The Russia-Trump collusion story is a total hoax, when will this taxpayer funded charade end?’ he wrote on Twitter on 8 May.
Until more information comes to light, Russia’s interference will likely continue to cause debate.