Backpack

The police acknowledged they're not sure he's from another country.

Police also released a sketch of the suspect and offered a 1 million baht ($28,000) reward for help leading to the arrest of the man they believe carried out Monday's bombing, which left 20 people dead and more than 120 injured. Authorities have called it the worst attack in Thai history.

"The yellow shirt guy is not just the suspect. He is the bomber," police spokesman Lt. Gen. Prawut Thavornsiri told The Associated Press.

Prawut earlier released several photos of the man, with and without the backpack, on social media. 

The images were apparently taken from closed-circuit video at the Erawan Shrine on Monday evening before the bomb exploded. He confirmed that the man is suspected in the bombing when contacted by The Associated Press.