Professional gambler Mehmet Hassan, 56, was last seen leaving Palm Beach, in Berkeley Street, on Sunday evening after winning £3,000 at poker.
He is said to have gone for a celebration meal at nearby Michelin-starred restaurant Nobu with a woman in her twenties before returning home to Islington.
His bound body was found in the bedroom of his locked flat at 8.40pm on Monday when his daughter called police after he failed to answer the door.
He was said to have kept at least £20,000 in cash in his second-floor flat on a former council estate in Baxter Road. Police say they are trying to establish what had been stolen from the property.
A worker at Palm Beach, which describes itself as the most exclusive casino in Mayfair, said Mr Hassan played poker at the club three or four times a week, spending hundreds of pounds.
Detective Chief Inspector Andy Partridge said: “I would like help from the public who can assist with the movements of the victim between 7.30pm on Sunday March 23, and shortly before police found him on Monday at around 8.30pm.”
The incident room can be contacted on 020 8358 0300.
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