An undercover officer, only known by her codename Lizzie James, was used to befriend suspect Colin Stagg into confessing to the murder on Rachel Nickell in 1992, who was stabbed 49 times in front of her young son on Wimbledon Common

The moment an undercover detective broke down under the weight of her role in the investigation into Rachel Nickell's murder has been recreated for an upcoming Channel 4 drama.