Thailand's police chief on Wednesday said the Bangkok bomb suspect was part of a "network" as the hunt intensified for the perpetrator of the country's worst-ever attack that left 20 people dead.

"The wrong-doer could not have been alone... we believe there must be people helping hiim, Thai people. It's a network," Somyot Poompanmoung told reporters, a day after the emergence of CCTV footage of a suspect leaving a backpack at the shrine just before the blast.