Investigators initially believed the bombing was the result of a conflict between gangs involved in extortion from roadside vendors.
Police said they were also holding one suspect under custody, however, they declined to give any information for fear of impacting the investigation.
Deputy Bangkok police chief Pol Maj-General Parinya Chansuriya Thursday said investigators were following the leads of four to five suspects after looking at CCTV footage. He said they were also checking the license plates of a Toyota Fortuna and Isuza pickup truck parked in the area.
The Nation