Dhaka, Sept. 24 -- Set off a crude bomb. Film the explosion. Send the video. Get paid.

Dhaka detectives say that is the simple formula behind at least some of the crude-bomb attacks that have rattled the capital over the past several days.

The Detective Branch (DB) says a "specific network" is recruiting people to carry out the blasts, offering between Tk 5,000 and Tk 10,000 for each explosion.

Instructions on where to go and what to do are being sent through WhatsApp accounts registered with Indian phone numbers, according to investigators.

The alleged operatives are told by text or voice call to detonate the device, record the blast, and send the footage back to the person giving the instructions. Only after the video arrives is the...