Ten suspects detained in the charter referendum letter case, some of them Pheu Thai Party members, were returned to Chiang Mai city from Bangkok on Tuesday for prosecution.
They are accused of printing and distributing 15,000 letters misleading people about the contents of the draft charter that goes to a referendum this Sunday.
The suspects were taken from the 11th Military Circle in Bangkok's Dusit district, where they had been held, to the Crime Suppression Division (CSD) as the first seven-day detention period under the National Council for Peace and Order (NCPO) edict ended. Police then took them to Chiang Mai to go before the military court there.
Authorities planned to ask the court to further remand them in custody.
The suspects included 44-year-old Tasanee Buranupakorn, former Pheu Thai MP for Chiang Mai and vice president of the Chiang Mai provincial administrative organisation, and her uncle Boonlert Buranupakorn, 59-year-old suspended president of the PAO.
Pol Maj-Gen Chayaphol Chatchaidej, commander of police criminal prosecution, told reporters at CSD headquarters in Bangkok that Ms Tasanee, Mr Boonlert, Pairat Maichomphu, also vice president of the Chiang Mai administrative organisation, and tambon Chang Phueak mayor Khachen Jiakkhajorn hired other suspects to print and distribute the letters in the northern provinces of Chiang Mai, Lampang and Lamphun. Authorities found the letters between July 12 and 15.
The other suspects were split into three groups. One group printed the letters, another distributed them to voters and the third group arranged the getaway.
There were altogether 12 suspects. Wisaroot Khunanitisarn was the first arrested for sending the letters, and his confession led to the arrest of the other suspects, Pol Maj Gen Chayaphol said. Mr Wisaroot had been detained in Chiang Mai since the start. Another male suspect, Thewarat Rinta, was still at large.
He also alleged that Tharnthip Buranupakorn, a younger sister of Ms Tasanee, was among the group helping people flee the area after distributing the letters.
The suspects were charged with sedition and collaboration in illicit activities under the Criminal Code, and with "distortion" of the content of the draft charter under the referendum law, Pol Maj Gen Chayaphol said.
It was earlier reported the letters falsely claimed that the draft charter would end free state school education along with health welfare and allowances for the elderly.
Mr Boonlert told reporters he denied all the charges.
Col Piyapong Klinphan, spokesman of the NCPO, said on Tuesday that soldiers had seized about 11,000 letters and some suspect confessed they had burnt about 4,000 other similar letters.