A high-rolling city banker was seen shrugging his shoulders and faking a sad face after murdering a high-class escort.
Zahid Naseem, 50, bludgeoned Christina Abbotts after paying her for sex.
Naseem, a father of two, initially told police he couldn't remember what happened during interviews in which he was seem pretending to look glum.
He was captured sitting with his arms folded and his head down before later resting his head on his hand and turning away from officers.
Christina suffered horror injuries as Naseem intentionally struck Mrs Abbotts 13 times on the back of the head with the kitchen utensil while she was house sitting for a friend in Crawley, West Sussex.
The freelance investment consultant, who could earn up to £250,000 in a year, claimed he acted in self-defence.
Expert analysis of his filmed police interview reveals clues to his web of lies.
Dr Cliff Lansley told Discovery's Faking it: "The claim he doesn't know is being contradicted by a single-sided shoulder shrug.
"This is subconscious, it's not intended for you to see."
A head shake, eye flickers and his posture also convinced investigators that Naseem was "very clear about what happened in that room and he's lying to us".
Lansley added Naseem showed his "first attempt at sadness" in order to get police on his side.
He said said: "When the brows raise and the mouth arches, it creates a signal of sadness. And when we feel it, that's what happens.
"But when you want to pose sadness, you can create the same arch and pretend you're sad to get pity and some mercy when you're in the wrong by jutting your chin and pursing your lip.
"If you ask a child to pose sadness, they do what we call a sulk, and this is what he's doing.
"He's doing a sulk pose on his mouth. His chin raises and his lip pouts out with a little frown.
"This combination is what we can pose sadness or sulking. It's not going to convince anyone to have pity at this point."
Christina, originally of Stourbridge, West Midlands, was found dead at the flat in May 2018 on her 29th birthday.
The court heard she is thought to have been dead for some 12 hours before she was discovered after she failed to turn up to her party.
She had met Naseem several times in her secret life as a high-end escort.
The defendant, who has two young children and lives in Amersham, Buckinghamshire, was said to have paid Christina up to £3,500 each time.
He told the court he turned to escorts when the "whirlwind romance" with his partner fizzled out and they grew apart.
For the best part of a decade, he hired sex workers, drank on an almost daily basis and took cocaine.
He said his job, which took him to New York, US, when working for Merrill Lynch, was stressful but he was "devoted" to his children and tried to spend all his spare time with them.
He was working for Toronto-Dominion Bank in London at the time of his arrest.
