Suspect Sakhon Kamto, 24, and her mother were released on Tuesday after signing documents saying they were willing to undergo the tests.

Sakhon is suspected of kidnapping one of the twin girls born to Ratree Trakanchan, 22, from a Lop Buri hospital last Friday.

Sakhon, who had an affair with Ratree's husband, confessed to stealing the infant. But she later retracted it, saying she had been forced by police to plead guilty.

Muang Lop Buri superintendent Colonel Thanyasit Amornsukon said an employee at a hotel in which Sakhon stayed had confirmed she used a shoulder bag similar to the one used by the kidnapper captured on the hospital's closed-circuit camera.