Man poses as customer to steal $35,000 diamond

A jewel thief patiently attended an appointment to look at diamonds, as part of his plot to nab a $35,000 gem.

The man, wearing a white shirt and glasses, strolled into the Californian jewellery shop earlier this month to discuss engagement rings.

CCTV shows a shop assistant showing him gems and carefully placing a loose diamond on his hand, before he covers it and sprints away.

"Cathy even took the time to straighten it on his hand," shop spokesman David McConnell explained, CBS San Francisco Bay reports.

"We put it on his hand and he covered his hand, and turned and ran out of the store."

The man ultimately made off in a green getaway car with paper plates.

The local Walnut Creek Police Department released the footage in a bid to identify the suspect.