Steve Fulcher is the real police detective who led the investigation. The series accurately portrays his pivotal decision to interview Christopher Halliwell without following all PACE guidelines, believing Sian O'Callaghan might be alive, and the subsequent professional repercussions he faced. The series is largely based on his memoir.

Christopher Halliwell is the real perpetrator convicted of the murders of Sian O'Callaghan and Becky Godden-Edwards. His portrayal as a seemingly ordinary man capable of heinous crimes, and his eventual confessions to Fulcher, are based on fact.

Sian O'Callaghan was the real 22-year-old woman whose disappearance in March 2011 and subsequent murder by Christopher Halliwell is the central case that initiates the events depicted in the series.

Becky Godden-Edwards (often referred to as Becky Godden) was a real young woman who had been missing since 2003. Her murder by Halliwell was revealed through his confession to Fulcher, a key factual element accurately portrayed.

Karen Edwards is the real mother of Becky Godden-Edwards. Her unwavering dedication to finding out what happened to her daughter and her fight for Halliwell's conviction for Becky's murder, even after legal setbacks, is accurately and prominently depicted.

Elaine Pickford (née O'Callaghan) is Sian's real mother. The series portrays her and her family's anguish and cooperation with the police during the search for Sian, reflecting the real-life events.

The series accurately depicts the real-life disappearance of 22-year-old Sian O'Callaghan after a night out in Swindon, which triggered a major police investigation.

Detective Superintendent Steve Fulcher was indeed the senior investigating officer in charge of the Sian O'Callaghan missing person case, and the series accurately portrays his central role.

Police work, including CCTV analysis and mobile phone data, led to taxi driver Christopher Halliwell becoming the prime suspect, and he was subsequently arrested. This is accurately reflected in the series.

This is a crucial and accurately depicted element. Fulcher made the controversial decision to take Halliwell to Barbury Castle and question him without a solicitor present and without formal caution, believing Sian might still be alive and her life was in imminent danger.

During the non-PACE compliant interview with Fulcher, Christopher Halliwell confessed to murdering Sian O'Callaghan and led police to the location where he had hidden her body. This is a factual event.

In the same period of questioning, after confessing to Sian's murder, Halliwell offered information about another murder and led Fulcher to a field where the remains of Becky Godden-Edwards were found. This is historically accurate.

Due to Fulcher's breaches of PACE, a judge ruled that Halliwell's confession to Becky Godden-Edwards' murder was inadmissible as evidence in court. Consequently, Halliwell was initially only tried and convicted for Sian O'Callaghan's murder. This is a key accurate legal point portrayed.

Steve Fulcher was investigated by the Independent Police Complaints Commission (IPCC), found guilty of gross misconduct for the PACE breaches, and received a final written warning. This ultimately led to his resignation from Wiltshire Police, all of which is accurately depicted.

The series accurately portrays Karen Edwards' persistent efforts and public campaigning to ensure Christopher Halliwell was brought to justice for her daughter Becky's murder, despite the initial legal setbacks.

After further police investigation gathered new evidence, Christopher Halliwell was eventually charged with, and in 2016, convicted of the murder of Becky Godden-Edwards and given a whole life sentence. This is accurately shown as the culmination of Karen Edwards' fight for justice.

The series is commended for its sensitive and respectful portrayal of the immense grief, anguish, and uncertainty experienced by the families of Sian O'Callaghan and Becky Godden-Edwards.

The series effectively explores the moral and ethical dilemma Fulcher faced: adhering strictly to police procedure versus taking unconventional action in a desperate bid to save a life, and the severe personal and professional consequences of his choice. This is central to the true story.

The series accurately reflects the timeline of Sian O'Callaghan's disappearance in 2011, the initial investigation, and the subsequent legal proceedings and final conviction of Halliwell for Becky Godden-Edwards' murder in 2016.

The events predominantly took place in and around Swindon, Wiltshire, and the series accurately uses this setting. Locations like Savernake Forest and Barbury Castle, which were significant in the real case, are featured.

The series provides a realistic insight into a major crime investigation in the UK, including search operations, forensic work, and the pressures faced by the police. The critical importance and implications of PACE (Police and Criminal Evidence Act) are central and accurately portrayed.

The depiction of the legal challenges, the role of the Crown Prosecution Service (CPS), the judge's rulings on evidence admissibility, and the trial process are reflective of the British legal system.

The series effectively conveys the shock and fear within the local Swindon community following Sian's disappearance and the subsequent revelations. The sense of ordinary life being shattered by horrific crimes is well captured.

While not a primary focus, the series implies the significant media attention and public interest that such high-profile crimes generate, which is consistent with real-life major crime investigations.

The clothing, cars, mobile phones, and other technology shown are consistent with the 2011-2016 period, contributing to the overall realism of the dramatization.

The series is noted for its sensitive and respectful handling of the tragic subject matter, focusing on the human cost of the crimes and the experiences of the victims' families, rather than sensationalizing the violence. This approach was supported by the involvement of Karen Edwards.