Airports of Thailand yesterday plays security-camera footage taken when a diamond ring mysteriously disappeared.

The 2.5-karat ring belonging to German tourist Richard Chrobop went missing after it entered an X-ray machine on the departure level on April 24.

Airport manager Serirat Prasutanond told a press conference that photo experts had confirmed that the X-ray picture captured an object that looked like a diamond ring and which appeared to be kept in a case.

The security-camera footage presented to the media showed that Chrobop had to pull out something from his pant's pocket twice, because the security gate sent off an alarm on his first two walk-throughs. Both times, he put the items in his jacket, which he placed in a basket to be passed through the scanning machine.

Picking up his belongings at the other end, Chrobop was unable to find what he had put in his jacket and spoke with the operator, who helped him search for it, but they could not find it.

Officials rescanned Chrobop's belongings but did not find the ring, which the first scanned image had shown, Serirat said.

The footage showed no airport officials touching tourists' bags or belongings, he said.

"If this is a theft, it likely involves many people, because one person can't take away valuables in such a short time," he said. If the incident is found to be the work of AOT staff, then the company will take fully responsibility, he said.