The Bt6.8 million deal was one of several GT200 sales involving a slew of state agencies and various distributors.
The armed forces insisted on the device’s efficacy even after it was proven in overseas tests to be useless in detecting anything.
Suttiwat was found guilty in a separate case last month involving the Royal Aide-de-Camp Department and sentenced to nine years in prison. The department had bought Bt9 million worth of GT200s and related supplies in 2010.
He and three other defendants in the latest case denied wrongdoing, but the judge found Suttiwat guilty and handed him another nine years in jail while ordering the firm to pay a Bt18,000 fine.
Two other defendants, both employees of Avia Satcom, were acquitted.