Police in Windsor say an alleged jewel thief they have in detention has finally passed a diamond that was stuck inside his intestinal tract for several days.

They say the stone "came out" on Saturday afternoon, nine days after a Precision Jewellers salesperson reported that a man had swallowed a $20,000 gem while pretending to be a customer.

He allegedly tried to switch a 1.7-carat diamond with a cubic zirconia.

Store employees confronted him and locked him in, and while police were on the way, they say he swallowed the diamond and two cubic zirconia stones. He expelled one of the fake gems on Friday.

Windsor police Staff Sgt. Dave Kigar told reporters on Sunday there's no need to wait for the second cubic zirconia to exit. Investigators and the man talked and they decided it would be more humane to transfer him to the county jail where he should shower and shave, he said.

Investigators spotted two of the stones inside the man after he was taken to hospital to undergo an X-ray. Kigar said a diamond does not show up in an X-ray because of its composition.

After his arrest, the suspect was held in a dry cell under close surveillance. He agreed to take laxatives and other fluids to assist in bowel movements.

Richard Mackenzie Matthews, 52, has been charged with theft over $5,000 and breach of probation. Kigar said Matthews will face an additional charge of possession of stolen goods over $5,000 when he appears in court.