Susanna Reid presents new doc 'The Murder of Becky Watts: The Police Tapes '

'The Murder of Becky Watts: The Police Tapes ' - a new documentary hosted by Susanna Reid airing on ITV tonight at 9pm - looks into how the detectives investigating the disappearance of Becky Watts came to the decision that her stepbrother Nathan Matthews and his girlfriend Shauna Hoare were responsible.

This morning, Ben Shepherd and Susanna Reid were joined by DCI Richard O'Cone who was part of the team that investigated the disappearance and death of the Bristol teenager. Watch the full interview above.

In exclusive police footage, the documentary reveals how forensic evidence and intense police interrogation led to revealing her killers.

Becky went missing in 2015, aged 16, in the St George area of Bristol. Her stepbrother and his girlfriend were the last who said they had seen her before she went missing, saying she had left “in a huff” even though they had murdered her by this point.

Nathan Matthews had murdered Becky and dismembered her body in what police have described as a sexually motivated killing. He was handed a life sentence for murder with Shauna Hoare given a 17 year prison sentence for manslaughter.

DCI Richard O’Cone said the pair "were callous” and had “put the family through days and days of unnecessary pain. They told a web of lies to take us away from the truth and evidence” and added that they were “cold and calculating”.

He described the case as the ‘‘most horrific I’ve ever had involvement with and it stays with you. I always reflect on the impact on the family.”

He also said that the police investigation “took some time and organised, meticulous evidence to come to try and get to the point where they become suspects. There were alarm bells early on, they were evasive and didn’t want to be interviewed as witnesses at that point or allow police access to the house, fairly difficult to nail down from an early point”

Watch the full interview above.

'The Murder of Becky Watts: The Police Tapes ' is on ITV tonight at 9pm.