Happy Valley's penultimate episode airs tonight — but will we come any closer to knowing who the serial killer is?

This series has left us guessing alongside CID officers as to who is behind the series of prostitute murders.

We examined the four possible suspects — Sean Balmforth, Neil Ackroyd, the Knezovich family and John Wadsworth — and this is how Examiner readers have voted so far:

Who is the serial killer?

Examiner poll

Clare's beau Neil Ackroyd is leading the poll, and ironically Sean Balmforth, arrested under suspicion of the murders, has only 7 per cent of the vote so far.

Neil Ackroyd (CON O'NEILL), Clare (SIOBHAN FINNERAN)
Neil Ackroyd (CON O'NEILL), Clare (SIOBHAN FINNERAN)

Debating the whodunnit on the Examiner Facebook page, readers have also put forward bullied farmer Daryl Garrs, played by Robert Emms.

Sophia Loizou said: "The farmer's son... had a hell of a lot of blue rope in the boot of his car!"

Sobia Ahmed Omar agreed: "It's the bullied kid off the farm. Did you not see what was in his car!"

Ann Gallagher, the victim of the kidnap plot in series one and now a PSCO, is also suspected by viewers it seems.

READ MORE: Happy Valley: 10 things we learned from episode four

Gayle Cruddace said: "I think it's the community support officer who was raped herself... She has become quite strange and actually finds seeing dead bodies interesting."

Ann Gallagher (CHARLIE MURPHY)
Ann Gallagher (CHARLIE MURPHY)

READ MORE: Who is the Happy Valley serial killer? We take a look at the suspects

There were some left-field suggestions:

Helen-Claire O'Connor said: "Hayley out of Corrie. I have a theory but no doubt [will] be way off."

Adam Hughes suggested: "What about her son? He cheated on his wife and turned up at her house, he doesn't really add anything to the programme and so I'm thinking 'why is he even there?' He could have moved in with his mum to find out any info she has about the case."

What do you think?

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Who is the serial killer?