Thailand's police chief says at least 10 people were involved in the Bangkok bomb attack that killed 20 people.
He also said the attack had been planned at least one month in advance.
"It is a big network. There was preparation using many people," police chief Somyot Poompanmuang said.
"This includes those who looked out on the streets, prepared the bomb and those at the site and ... those who knew the escape route," he said.
"There must have been at least 10 people involved."
Police had already said they were looking for three suspects, including a young man in a yellow T-shirt seen on grainy video footage apparently planting the bomb.
That man could be a foreigner, according to authorities, who also released a sketch of the suspect.
One Briton was killed in Monday's bombing at the Erawan Shrine, which also wounded 120 others.
Nobody has claimed responsibility.