BANGKOK: A key suspect in last month’s deadly Bangkok blast handed the backpack bomb to a man in a yellow T-shirt later seen placing it at a busy shrine moments before it detonated, Thai police said Wednesday.

The revelation came as investigators gave their most detailed account of how the alleged network of bombers coordinated the attack, including through drop-offs and WhatsApp text messages.

Mystery still surrounds the motive of the group accused of being responsible for the Aug. 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, police have trumpeted the arrest of two foreigners and say they have identified several other suspects.

One of the two men in custody, Yusufu Mieraili, was detained last week near the border with Cambodia and has since been quizzed by military and police investigators.

Mieraili, 25, who was holding a Chinese passport when he was caught, has admitted to playing a central role in the operation, according to police.

On Wednesday he was taken on a second re-enactment of his alleged role in the crime — a standard police procedure.

“This is the area where he met the man in a yellow shirt to exchange the backpack,” national police spokesman Prawut Thavornsiri told reporters outside a Bangkok railway station, later adding he received his orders via WhatsApp.