Pirates are thought to have drowned 16 fishermen in southern Bangladesh in order to steal their boat.
Their hands and feet were bound before the victims were thrown into the Bay of Bengal to drown, police said.
The bodies had no injury marks, local deputy police chief Imran Bhuiyan told AFP, prompting speculation the men had been thrown into the water alive.
A fishing boat recovered three bodies while 13 were seen floating in the water off Kutubdia Island, he added.
Police and navy officials were using the help of fishermen to recover the remaining bodies.
"Three dead bodies have already been brought to the shore. Two navy ships are now searching the bay for other missing fishermen," a Bangladeshi naval official told the BBC's Anbarasan Ethirajan in Dhaka.
"Sea robbery is more or less common in that part of the sea. But killing... in huge numbers like this, is not a common phenomenon."
Concerned relatives have joined the search for some 30 fishermen from the Bashkhali area - near Chittagong and some 300km (190 miles) south-east of the capital Dhaka - who set sail last week.