A Great Falls jeweler was convicted this week of swapping out diamonds in customers’ rings with cheaper stones in a scam that netted nearly $50,000 worth of jewels.

Robert Mikail, 40, of Ashburn, entered Alford pleas on nine counts of grand larceny and grand larceny with intent to sell in Fairfax County Circuit court.

In an Alford plea, a defendant admits there’s enough evidence for a conviction but doesn’t admit guilt.

Mikail, who owns Vima Jewelers, was arrested last July following a sting at his store on Seneca Road, Fairfax County police said.

An undercover officer took about a dozen pieces of jewelry to Vima to be appraised, police said. After the officer picked the pieces up, another appraiser determined a diamond on a ring had been replaced with a lower quality stone, police said.

When police returned to Mikail’s store to arrest him, they found the diamond on his workbench, prosecutors said.

Police staged the sting after a complaint from a 23-year-old woman in April 2011.

The woman said she had taken her collection of jewels to Vima for appraisal, but discovered that a necklace and pendant worth $1,000 were missing when she returned home, police said. Police later identified four other victims.

Mikail entered Alford pleas on the five grand larceny charges before the trial began, but withheld pleas on the grand larceny with intent to steal until later in the trial.

Defense Attorney Peter Greenspun said during his opening statement prosecutors did not have evidence that Mikail intended to resell the jewels he had taken.

In her opening statement, Assistant Commonwealth’s Attorney Lena Munasifi said Mikail established good relationships with some of the victims, before taking their diamonds.

“She thought he couldn’t have robbed her because he was a friend,” Munasifi said of one victim.

Mikail is scheduled to be sentenced on Dec. 14. He faces a maximum of 90 years in prison, but will likely get a much lighter sentence.