Anthony Clapham, 31, stayed behind when other punters left after the last race and then repeatedly stabbed Sian Collier, 24, in her office before fleeing with pounds 400.
He deceived his wife into thinking his money was holiday pay from work as a lorry driver, Christopher Pitchford, for the prosecution, told Newport Crown Court in Gwent.
Two hours after the murder, Mr Clapham hired a car and took his wife and their two-year-old daughter on holiday to the home of his parents-in-law in Dorset.
Unknown to his wife, Mr Clapham had during the day placed 14 different bets, costing nearly pounds 135, in the Ladbroke shop in Corporation Road, Newport, and at another betting shop in the town. But only one had brought him any money, Mr Pitchford said.
The gambler, spending half the family's joint income on his addiction, secretly emptied a joint building society account which was intended to buy a house, and failed to make any repayments on a pounds 2,000 loan.
Mr Pitchford alleged that Mrs Collier was stabbed in the back and also strangled with a telephone cord because she could have identified Mr Clapham as one of her regular customers. He struck as she worked alone, cashing up the day's takings in her back office, on 25 August last year.
Police found her body after she failed to return home and her husband raised the alarm. Mr Clapham, who denies murder, told police he left the shop after the last race. But forensic science evidence found at the scene was 'proof positive' that he was the killer, Mr Pitchford told the jury.
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