It was unclear on Monday whether he would be brought to a military or civilian court.
Wattana surrendered to the Army on Friday evening as police considered applying for an arrest warrant for him in relation to the weapons.
He was detained at the 11th Army Circle base under the interim charter’s Article 44 order prohibiting the possession of military weapons, Srivara said.
Initial questioning allegedly discovered Wattana’s links to “hardcore red shirts” and his previous record of possessing unauthorised military weapon, Srivara said.
Wattan’s seven-day detention under Article 44 ends on Thursday, so he will be brought to court to extend his detention.
Police were also gathering evidence to apply for an arrest warrant for another person linked to the case, Srivara said.
In 2014, Wattana was arrested for possessing military-grade guns, ammunition and explosives following the apprehension of Somjet Khongwattana, who allegedly had distributed weapons to create chaos during protests.
At the time, Wattana confessed to receiving weapons from Somjet to redistribute, including to another suspect, Chaiwat Polpho, but he then reportedly dumped the weapons in Ayutthaya’s Lat Bua Luang district after the junta announced plans to punish people for weapons possession.
Meanwhile, national police chief Pol General Chakthip Chaijinda dismissed speculation that the discovery of the weapons in Chachoengsao was a false flag operation.
Chakthip said he would not comment on politics, but added that the speculation that the discovery had been a set up was untrue because Srivara, who oversees national security, “would not do it” and the weapons were real.