The security system at Suvarnabhumi Airport did not detect a handgun belonging to retired city police chief Lt General Camronwit Toopkrajank when he left the airport for Japan on June 18.
Camronwit is in detention in Japan after a gun was found in a bag he carried as he was about to leave Tokyo for Bangkok on Monday.
Suvarnabhumi Airport deputy director Phet Chan-charoen said both passenger and luggage have to pass security screening at the airport before leaving the country.
"A passenger [would] walk through an x-ray machine while luggage [would] go through a bomb detector, or CTX, which would focus the screening on explosives only," he said in a press conference.
Asked if the CTX machine could detect a gun, Phet said it would identify it only as a metal object which would not pose danger to the plane, he said.
Earlier it was suspected that Camronwit may have bought the gun in Japan. However, Thai police spokesman Pol Gen Prawut Thawornsiri told reporters that Camronwit had the gun from long before he retired. His son is now in Japan to show a registration document to Japanese police.
Observers said this showed Camronwit brought the gun in question with him from Bangkok - only to be detected in Japan. Security systems of the Airports of Thailand that oversee Suvarnabhumi Airport have been criticised for not being adequate enough to detect the gun.
However, Phet said if the gun was in Camronwit's case, the CTX might have been unable to detect it as the machine was a bomb detector and because the gun was very small. "According to US standards, [if a metal item] is found [stored] under the plane, it is not dangerous as a passenger has no access to get to it to do harm to the flight."
When told that Camronwit was found with a gun and five bullets, which are explosive items, Phet said they may have been a small volume only. "We have to focus on the power to destroy and [cause] disaster," he said.
Meanwhile, Public Affairs Division director Pol Maj General Apichart Suribunya said Japan's public prosecutors might spend a few more days before concluding Camronwit's case.
It is believed that Japan uses the same procedure as Thailand's in investigating such cases, so more time is required.
Apichart said he had learned that Japanese police had handed Camronwit to public prosecutors on Wednesday. His division has contacted their Japanese counterparts and asked for updates on the case. But the procedure would take time, as it was not easy to translate from Japanese to English.