During the day they pose as day labourers working in the fields and dredging the riverbed. Under the cover of night, they become members of notorious robbery gangs.
They wait for the leaders' call to launch heists, and their primary targets are jewellery stores.
The robbers' gangs have used the waterways and speedboats to rob more than 50 jewellery stores across multiple districts in the last three months.
Among these robbed jewellery stores, 11 are in the Matlab area of Chandpur, six in the Bakerganj area of Barishal, four in Muladi and 13 in the Kaliganj and the Sreepur areas of Gazipur and one in Araihazar.
On January 22 this year, a gang committed a series of heists at Chandpur's Matlab Thana area. The robbers held police and security personnel hostage, then stole 78 bhori of gold, 100 bhori of silver and a large amount of cash.
The police launched a thorough investigation after noticing a significant increase in such robberies of late.
Senior police officials have also directed district superintendents of police, the Police Bureau of Investigation (PBI) and the Criminal Investigation Department (CID) to curb the crimes and bring those responsible to justice.
The CID arrested four members of a gang from Lakshmipur and Shariatpur's Jajira area between January 3 to 7 over the robberies in Chandpur. The arrested people are Sobuj, his wife Akhi Begum, Monju and Danesh.
Law enforcers also seized a speedboat used for the robberies, said sources.
Sobuj confessed at court to committing the crimes. Based on his statement, police have arrested more than a hundred members of 5 gangs in cases filed over the robberies.
According to sources at the CID, two masterminds behind the crimes have been identified. These two people led the robberies at dozens of jewellery stores across the country.
The members of the five gangs are well trained and organised, and they get Tk30,000 in cash after committing each robbery.
The CID's Additional Superintendent of Police Rajib Farhan told The Business Standard, "We learnt the names of other members in the racket on questioning the arrested four. We are making an effort to take them into custody."
Investigators said that a case was filed over the robbery in the Sreepur area of Gazipur on December 16 last year. Police have arrested 11 of the alleged robbers, and six of them have confessed at court.
Police have also arrested one person over a robbery in Kaliganj upazila under Gazipur district, and 20 people over a robbery in Bakerganj. One of the 20 has confessed at court.
Besides, police have arrested eight people over a robbery in Muladi.
How robberies were commited
The gangs pick targets in areas adjacent to waterways, especially jewellery stores in markets near the banks of rivers. Each gang comprises of 10-35 trained robbers.
The gangs use speedboats with double-engines to reach their destinations, and carry bombs, cocktails (crude bombs) and locally-made firearms.
They enter a market disguised as police or Detective Branch personnel and then take the local security personnel hostage almost immediately.
Then they begin to empty out the jewellery stores. If a police patrol team enters the market, the robbers also take them hostage and tie them up.
After robbing jewellery stores, they use bombs and cocktails to clear any gathering of people in the market area and make a quick escape to an adjacent district using the speedboats.
CID's Additional Superintendent of Police Rajib Farhan said that the robbers chose the waterways method because is it easier to escape the authorities using speedboats.
"The robbers choose targets in markets of districts that are very close to other districts. After a robbery, it takes them only a few minutes to cross over to a nearby district. For example, Chandpur is very close to Shariatpur and Munshiganj," said Farhan.
Police instructions on curbing robbery
The police headquarters has given a number of directives to authorities concerned for curbing such robberies, such as the formation of new lists by district police, PBI and CID to identify new robbers' gangs, and evaluating those lists through coordination meetings.
Police headquarters has also ordered the formation of special teams comprised of superintendents of police from districts where the robberies are being committed, and the carrying out of regular raids.
The district police will spearhead a drive to locate and confiscate firearms being used in the robberies, with the Rapid Action Battalion (RAB), CID and PBI providing additional support.
The police are also advising jewellery store owners to install CCTV systems in their shops, and to keep the gold and jewellery in iron chests or safes after each day's sales.
Local people should also form defence parties to protect the markets. More lights should also be installed in markets and patrols on waterways should be increased.
Police were instructed to make a list of all speedboats in every district across Bangladesh, and monitor the owners of those boats after getting their names, addresses and mobile phone numbers.