ITV’S primetime drama about the Christopher Halliwell murders concludes at 9pm tonight. This is the story so far.

Sian O’Callahan went missing in the early hours of March 19 2011 on the way home from a night out. A police investigation into her disappearance lead to taxi driver Christopher Halliwell (played by Joe Absolom) becoming a suspect.

Halliwell was arrested while buying painkillers from a Swindon pharmacy, but instead of reading him his rights and taking him into custody, detective superintendent Steve Fulcher (Martin Freeman) conducted two urgent interviews.

This questioning near Badbury Castle prompted Halliwell to confess to Sian’s murder, give tell officers exactly where he left her and unexpectedly disclose the location of another body.

Forensics proved that Halliwell’s second victim was Becky Godden-Edwards, who went missing in 2003. Her mum Karen held out hope for years that her daughter was still alive.

Though initially hailed as a hero, Fulcher suffered a series of setbacks upon his return to Gablecross police station.

He was scolded by his superiors for breaching police guidelines after Halliwell gave no comment interviews and refused to approve a transcript of his confessions.

These confessions were then unusable as evidence in court and as a result Halliwell could not be found guilty of Becky’s murder.

Fulcher was found guilty of gross misconduct despite a surge of public support and resigned from the force.