SAINT JOHN, N.B. -- Daring thieves stole a $10,000 diamond in a split-second switch with a fake, a New Brunswick jeweller says.

"These were pros," said Wayne Smith, owner of W. Smith and Co. Fine Jewellers in Saint John.

Smith said the thieves -- presenting themselves as a middle-aged couple -- came into his store shortly before closing last Friday.

Although Smith wasn't there, he said the whole thing was caught on remarkably clear video surveillance cameras.

They asked to look at a loose, one-carat diamond valued at $10,000, then began to argue, clearly trying distract the saleswoman, Smith said.

The man asked to see another diamond, a 1.5 carat stone worth $25,000, and made his move while she reached for a comparison chart.

"He was very quick. You will see him (on the video) drop the fake stone and grab the real stone and slide it in his back pocket. They tried to get the second stone and that's when she caught them. And it was only after they left the store that she went back to the first stone, and realized they got us," he said.

"And then we went onto the camera system, and it was very clear. Once you see it, you'll go 'Oh my God."'

Smith, a one-time vice-president of Birks jewellers for Atlantic Canada, said thefts are not uncommon at jewelry stores, but they're usually kept quiet.

He says he decided to speak out because he was angry, because his insurance deductible is so high it won't cover the loss, and because the video is so clear the public can help nab them.

"I've been in the business 40-some years and most jewelry stores don't talk about it," he said.

"I know of robberies in Halifax that they never went public ... the companies just want to hush it. And I went no, I'm going to tell people, show them who they are and maybe prevent them from hitting somebody else."

Smith said he has instituted a new policy at his store: customers must show picture identification before they can be shown a loose stone.

Saint John police did not return a phone call Thursday, but Smith said their investigators combed through photos of every cruise ship passenger in Saint John at the time in a bid to find the thieves.

Smith said he now believes the thieves were locals, and thinks surveillance images are so clear they will be found. He has offered a reward for information that leads to their identification.

"This is my store, this is my business, and this is my love. And my inventory is like my family. I know it all. I take a lot of pride when I sell somebody a ring, and it's got my name on it. And when that happens and somebody steals that from you, yeah, you feel violated."

-- By Rob Roberts in Halifax.