An investigation into corruption by senior Immigration Bureau (IB) officers has found clear evidence of some officers helping foreign criminals, and even serving as owners of foundations that arranged visas for Chinese nationals.

One of the foundations had its headquarters in a chicken coop, police said.

They found clear proof of offences such as renewal of visas for Chinese nationals through foundations, visa applications by schools or the falsifying of signatures of a deputy governor.

Some officers had used houses and the chicken coop as offices for foundations set up to apply for visas for Chinese nationals. Investigators found some IB officers were owners of foundations that hired agents to falsify documents, police said.

Police are expected to summon all of the accused officers, ranging from commanders and station heads to officers at the operational level, to hear the charges next week.

The former massage parlour tycoon and politician Chuvit Kamolvisit for weeks has been supplying police and the media with documents said to detail links between corrupt officials and grey businesses run by Chinese triads in Thailand.

He alleged that three former division commanders of the Immigration Bureau took bribes in exchange for approving non-immigrant visas for 3,325 Chinese nationals who had entered the country on tourist visas.

He said the cost of getting such an application approved by one of the commanders ranged from 100,000 to 300,000 baht per person.