THIS is the chilling moment Shauna Hoare smiles as she gets a thrill out of lying to cops after butchering her killer boyfriend's step-sister Becky Watts.
The schoolgirl was suffocated by her stepbrother Nathan Matthews and his girlfriend Hoare, who chopped up her remains and stashed them in suitcases.
The couple lied through their teeth in chilling police interviews during a futile 12-day missing person search for Becky in February 2015.
Harrowing footage shows Hoare getting a thrill as she tries duping cops as her and Matthews spin a web of lies.
But experts on Investigation Discovery's Faking It: Tears Of A Crime have revealed how Hoare gave away tell-tale signs while being grilled by cops.
Cliff Lansley points out Hoare smiles as she's asked about Becky's disappearance, saying: "This is what we call ‘duping delight'; it’s the thrill you get from getting away with a lie.
"Those little smiles, she can’t control them… she thinks she’s winning here."
The body language expert has also suggested Hoare, who was convicted of manslaughter, was the main instigator of the brutal killing.
He said: "Matthews may be the instrument, but like Lady Macbeth, Hoare goaded him into it and was pulling the strings.”
In February 2015, police were closing in on the evil pair as they frantically searched for Becky in Bristol.
Cops went round to the couple's Bristol home and found a shiny clean bath among the piles of grubby furniture and rubbish in the other filthy rooms.
This aroused their suspicions the schoolgirl had been murdered as the warped couple's web of lies began to unravel.
It was in the gleaming bath the depraved couple dismembered Becky using power tools before stashing her remains in the suitcases.
They were arrested on February 28, nine days after the murder, on suspicion of Becky's kidnap.
Following a forensics search of Becky's home Matthews fingerprints were found within traces of her blood on the door frame of her bedroom and the couple were re-arrested on suspicion of murder on March 2.
Matthews buckled and wept through a police interview later that day in which he admitted killing Becky.
But he still put their heartbroken families through the ordeal of a trial by lying that he hadn't murdered her, but killed her accidentally in a fake kidnapping which went wrong.
Hours later, her body parts were found in the shed of their friend Karl Demetrius around 80 yards away from their home.
Matthews suffocated Becky in her bedroom while Hoare waited downstairs and the pair then moved her body to their own home before dismembering her.
He was convicted of murder and Hoare found guilty of manslaughter by a jury at Bristol Crown Court.
Tomorrow's episode also explores Grindr killer Stephen Port, who was caged for life in 2016 after being convicted of drugging, raping and killing at least four men.
The experts reveal how Port gave away six tell-tale signs while being interviewed by police - including signs of anxiety such as an itchy nose and a drop in volume.
Professor of Linguistics Dawn Archer said: “Guilty speakers will use more negation… his volume drops, which suggest that the words he’s saying aren’t matched by a level of confidence.
"In other words, he’s not believing the no’s as he’s saying them.”