They can strike at any time -- day or night as Rafiq Ahmed, a government official, found out on his way to visit his ailing uncle at the Dhaka Medical College Hospital (DMCH) last week.

"One of them put his hand over my mouth while the others started to punch me. That was the last thing I remember. When I gained my senses the next day, I found myself lying in a hospital bed," said Ahmed whose cellular phone and wallet were taken away when he was intercepted at the Mohakhali crossing by three miscreants.

His story is all-too familiar to doctors.

"Miscreants nowadays make people senseless and take away their belongings," said ABM Moshiul Alam, a duty doctor at the emergency department of DMCH. "They use chloroform and sometimes inject other chemicals like morphine and pethidine," he said.

"We receive at least five cases during day and the numbers go up to ten between 10 pm and 5 am," added Dr Alam.

Hospital sources said even a half-an-hour journey from Mirpur to Gulistan could risk somebody being easy target. Most of the victims are poor rickshaw-pullers who accept food from unknown people without asking questions.

It is suspected that miscreants also use thorn apple (dhutra) powder.

"As the powder has no taste, colour and smell, it is very easy to use. A small dosage is enough to make the person senseless for 5-10 minutes," he added.

The passengers are not the only sufferers -- it applies to CNG drivers as well.

"Criminals offer spiked drinks or food to the drivers and then take over their vehicles. Around 15 CNG auto-rickshaws are hijacked in the capital a day," said Mohammad Helaluddin, sub-inspector of Tejgaon police station.

"We are frightened by these miscreants and cannot ply on the streets freely. It takes around Tk 50,000 to 60,000 to get an auto-rickshaw back from the gang," said Babul Akhter, a CNG driver in Rampura.

On the other hand, commuters allege that CNG drivers themselves have links with the criminals.

"All of a sudden the driver stops the vehicle on a lonely or unlit stretch of road pretending that the engine needs fixing. Then suddenly the miscreants appear and disappear in the same vehicle," explained one commuter.

Whatever mode of transport is used the aggyan gangs can find ways to make one's life miserable.

"Criminals also target passengers of black cabs," said SI Helaluddin.

"More than one group operate in the city. No matter how many times they are arrested, these criminals commit the same offence once they get out," Helaluddin added.