A key suspect in last month's deadly Bangkok blast handed the backpack bomb over to a man in a yellow T-shirt later seen placing it at a busy shrine, Thai police said Wednesday, according to AFP.

Mystery surrounds the motive of the alleged network behind the August 17 bombing that left 20 people dead in the heart of Bangkok and rocked Thailand's key tourist industry.

But after appearing flat-footed in response to the unprecedented attack on Thailand, police have trumpeted the arrest of two foreigners and say they have identified several other suspects.