By The Nation
Investigators had obtained sufficient scientific evidence to ask the court to approve arrest warrants against four more suspects, the source said on Saturday.
The source said deputy national police chief Pol General Srivara Ransibrahmanakul would also visit Songkhla next week to check the progress of the investigation.
A group of Muslim insurgents robbed a used-vehicle tent in Nathawee on August 16 but police later managed to retrieve the stolen vehicles.
During a shootout with troops and police, an insurgent was killed together with an employee of the used car firm who had been taken hostage. Another worker was injured.
Police earlier obtained arrest warrants for six suspects. One has surrendered.