Elaine O'Hara, a 36-year-old Dublin childminder, was murdered by Graham Dwyer, a seemingly respectable architect and father-of-three, in August 2012, yet the case nearly went unsolved. For 14 months after her death, Dwyer believed he had committed the perfect murder, but unseasonably dry weather in August 2013 caused water levels at Roundwood Reservoir in County Wicklow to fall dramatically, exposing evidence he had hidden. The discovery of keys bearing O'Hara's supermarket loyalty fobs, along with sex toys and clothing, proved to be the critical breakthrough that ultimately led to his arrest in October 2013 and the unravelling of what investigators would reveal was a manipulative BDSM relationship between predator and victim.

The investigation faced significant challenges owing to the forest location where O'Hara's remains were eventually discovered on Killakee Mountain, with only 65 per cent of skeletal remains recovered and an undetermined cause of death. Detectives, led by Detective Sergeant Grace O'Boyle and Detective Sergeant Kevin Duggan, had to rely almost entirely on digital forensics—CCTV footage, mobile phone records, text messages and witness statements—to construct a comprehensive timeline of O'Hara's final movements and establish Dwyer's involvement. Her body had been found approximately 13 months after she disappeared, having been placed near a cemetery where her mother was buried, a location she had visited with her father on the day she went missing.