Police said the raids were in response to a crimewave in the central province in which Pol L/Cpl Sahachart Theungsook, who was attached to the Royal Thai Police's (RTP) Special Branch Division 3, was killed on May 10.
Pol Col Akkaradet Pimolsri, acting commander of the Crime Suppression Division, led a 20-strong commando force to search Mr Chaiya’s house about 5am on Friday.
The raid on Mr Chaiya's house uncovered eight handguns, more than 800 bullets of 9mm, 11mm and .45 calibre, two radios and a bullet-proof vest.
Chatchai Yuyatmak, an assistant village head who was also Mr Chaiya's driver, allegedly said the vest was his but could not remember the name of the person who gave it to him.
Police said Mr Chaiya cooperated fully when he was presented with a search warrant.
The raid on Mr Chaiya's home came after police received a tip-off that his close aides were linked to several violent incidents in the province, police said.
The former commerce minister was later invited for questioning. Police said he denied allegations that his close aids were killers, insisting all his employees have clean records. Police have neither detained nor pressed charges against Mr Chaiya.
Mr Chaiya’s home was among 13 locations raided, with all the properties belonging to prominent figures and suspected gunmen in Nakhon Pathom, police said. More than 200 police commandos were involved in the operation.
Police also searched the main office of Thai Wutthipong Co on Ratmakkha Road in Muang district.
The land levelling firm is owned by Wonchai Eakwichaphong, village head in tambon Phra Pathom Chedi of Muang district.
Police found Ratthakorn Jaenkitnarong, alias "MP Bae", a former Pheu Thai MP, in the office at the time of the raid.
A .38 calibre pistol, a wooden club and several car licence plates found in the office were taken away for examination.
Mr Ratthakorn was also invited for questioning. No charges were laid against him.
In total, 19 handguns, six rifles, ammunition, 16 car licence plates, a bullet-proof vest, two radios, and 80 football gambling records were confiscated during the raids.
All weapons will be checked to determine if they had been used in crimes.
Four suspects were also apprehended. Three were charged with illegal possession of a firearm and another with illegal gambling on football.
National police chief Pol Gen Somyot Pumpunmuang recently signed orders shunting 21 senior officers in Nakhon Pathom.
The orders stated the transfers were in response to several violent incidents in Nakhon Pathom province, particularly on May 10 and May 19 in which Pol L/Cpl Sahachart and gambler Somsak Saengthong were murdered.
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