Unforgotten viewers claim they've ALREADY identified the murderer just halfway through the crime drama thanks to string of obvious clues in first three episodes - but who do YOU think did it?

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Unforgotten viewers have been left divided by ITV's cold case drama as many suggest they already know who was behind the victim's death following the first three episodes. 

The decapitated body of Matthew Walsh, a young man who went missing in March 1990, was found in a freezer at a scrapyard and investigated by detective DCI Cassie Stuart (played by Nicola Walker) and her colleague DI Sunny Khan (Sanjeev Bhaskar) in the first episode.

Speculation was soon rife about the identity of the killer, with last night's episode offering even more clues as to which of the four suspects is guilty -  with some viewers of the British drama suggesting all of the potential killers, who knew the victim, are to blame.

The suspects include father-of-two Ram Sidhu, career woman Liz Baildon, therapist Fiona Grayson and successful businessman Dean Barton, who were all training to become police officers before mostly changing their careers.

While some fans suggest they all had a role to play in the killing, many believe intelligent career-striven Liz is the mastermind, thanks to her mother suggesting she has secrets galore, and her nervous performances when chatting to DCI Cassie.  

Unforgotten viewers have been left divided by ITV's cold case drama as many suggest they already know who was behind the victim's death. Pictured, Susan Lynch as suspect Liz

The decapitated body of Matthew Walsh was found in a freezer at a scrapyard in the first episode. Speculation was soon rife about the identity of the killer, with last night's episode offering even more clues as to which of the four suspects (pictured suspect Dean) is guilty

The fourth series, which comes three years after the last one, sees the dissected body of Millwall Football Club supporter Matthew Walsh discovered in a scrap metal yard after having spent 30 years in a domestic freezer.

The appliance belonged to a recently deceased man, Robert Fogerty, who was caught drink driving the same night the victim vanished.

Detectives also discover there were four other passengers - who are thought to now be the main suspects in the case - in Fogerty's car that night.

Fogerty and the four passengers were brand new police officers on their way home from a party.

The four suspects, now all in their late forties with mostly happy lives, include father-of-two Ram Sidhu (Phaldut Sharma), who is a successful businessman, living with his wife Anna in London. They are expecting their first child together.

The suspects include father-of-two Ram Sidhu (pictured), career woman Liz Baildon, therapist Fiona Grayson and successful businessman Dean Barton, who were all training to become police officers before mostly changing their careers

While some fans suggest they all had a role to play in the killing, many believe intelligent career-striven Liz is the mastermind, thanks to her mother suggesting she has secrets galore, and her nervous performances when chatting to DCI Cassie. Pictured, Fiona (Liz White)

Another suspect is academic Liz Baildon (Susan Lynch). She and her fiancée Janet are based in Cambridge, where she rides around on a bike and combines work and home life with the considerable demands of her ageing mother, played by Sheila Hancock.

Therapist Fiona Grayson (Liz White) has a practice in the Peak District, where she lives with her partner Geoff and their children, and is the third suspect.

While the fourth is Dean Barton, another successful businessman, who shares a home in Rochester, Kent, with his wife Marnie, their disabled son, Jack, and his younger brother, Casper.

After last night’s episode, some viewers suggested all four were involved with the murder, pointing out how Ram easily squashed a formal complaint made against him, while Dean appeared rather suspicious-looking.

Liz and her fiancée Janet are based in Cambridge, where she rides around on a bike and combines work and home life with the considerable demands of her ageing mother, played by Sheila Hancock (pictured)

The murder is being investigated by detective DCI Cassie Stuart (played by Nicola Walker) and her colleague DI Sunny Khan (Sanjeev Bhaskar), pictured together

Meanwhile, Fiona suffered a fleeting flashback which saw her being intimate with a man, leaving fans to suspect she could’ve been assaulted by Matthew Walsh.

But it is Liz who seems to be a clear contender for the role of mastermind in the murder, with viewers suggesting her mother’s concerns over her secrets, and the character’s nervous performances all point to her being the killer.

Taking to Twitter, one fan wrote: 'Liz is the smartest one in the group... she knew what to do, hiding the most important part of the body and keeping the whole story buried for 30 years. She wasn't just behind the wheel, she was the brains behind the whole crime.'

Another said: ‘Liz’s mum played by Sheila Hancock said "I could tell you some things about our Elizabeth that would make your hair turn grey". I wonder what secrets she knows about Liz.'

Reaction: It is Liz who seems to be a clear contender for the role of mastermind in the murder, with viewers suggesting her mother’s concerns over her secrets, and the character’s nervous performances all point to her being the killer

A third added: 'If we have learnt anything is that Liz definitely thinks a step ahead, she definitely came up with the idea to cut the hands and head.'   

'There's got to be a reason why Liz rides a bike now - they all think they killed him or could've killed him,' a fourth wrote. 

Other viewers believed all four were guilty, with one person writing on Twitter: 'Definitely all involved,' while another said: 'I'm feeling Fiona but now thinking they all have keys to something being stored so perhaps all of them are guilty.'

A third wrote: 'Walsh did something awful to Fiona and the others rushed to her defence? Only it got out of hand.'

 After last night’s episode, some viewers (above) suggested all four suspects were involved with the murder, 30 years ago

Unforgotten continues on Monday, March 15 at 9pm on ITV.