OKLAHOMA CITY (Reuters) - A man dressed as a security guard walked out of an Oklahoma Wal-Mart with $75,000 in cash, a crime that went undetected until the real security guards showed up later to transport the money, police said on Monday.

The suspect walked into the Wal-Mart on Saturday in Bristow, southwest of Tulsa, dressed in clothes similar to those of a Loomis armored truck employee. He went to the cash office, signed a deposit slip and walked away with the money, Bristow Police said.

Police were called when the real Loomis personnel arrived less than an hour later with no cash to transport.

Oklahoma authorities and the Federal Bureau of Investigation are searching for the suspect, which video surveillance showed getting into a black Chevrolet Malibu and driving off from the store with the money.