Police asked the Bangkok South Criminal Court on Monday for arrest warrants for seven suspects connected to the case.
Four suspects have been detained, while the police remain in pursuit of three other suspects who are still at large.
Royal Thai Police acting commissioner Pol Gen Watcharapol Prasarnrajkit and Deputy Commissioner Pol Gen Somyot Poompanmoung announced the arrests of Taweekham Wichakham, Sunthorn Pipuannok, Chatchawarn Prapbanrung, and Somsri Marit on eight charges, including attempted murder and connections with explosions.
The police made the arrests in the Sai Mai area, during which they also confiscated evidence including three pick up trucks, an M-79 grenade launcher, 25 M-79 grenades, one M-16 assault rifle, 70 M-16 cartridges, and five hand grenades.
All four men admitted to committing the crime in February, and that they were hiding out in theSai Mai area to lay low.
During the gruesome act, the suspects used the three pickup trucks found at hide out to drive to the crime scene, where Mr Taweechai was the person to fire the grenades into the crowd from inside the vehicle.
The M-79 was fired in front of Big C Supercentre, a discount store and food outlet in the Rajdamri area, near the PDRC's protest site back in February.
The explosion killed three people who were out shopping, including two children, and injured 21 others mingling in the street.