All efforts of detectives to track down criminals involved in extortions and issuing various threats over cellphones are going in vain due to their use of fake registration for mobile SIM cards and fake international mobile equipment identity (IMEI) numbers.

Despite rise of extortions and death threats using cellphones by criminals, law-enforcers and Bangladesh Telecommunication Regulatory Commission (BTRC) can do nothing against them as the authorities concerned can only lock those SIMs.

Detective Branch (DB) officials said they were forced to request the BTRC authorities for taking immediate measures to deal with the problem when it turned alarming.

BTRC officials said they so far have locked a total of 3,491 SIM cards of different mobile phone operators after receiving complaints against those SIM card holders for issuing various threats and demanding tolls since September 2008.

Meanwhile, the home ministry formed a committee headed by the BTRC chairman in the beginning of October following requests from law-enforcement and intelligence agencies for stopping rampant use of fake identities in mobile SIM registration process.

Talking to The Daily Star, BTRC Chairman Zia Ahmed admitted the rampant use of fake identities in SIM registrations and fake IMEI numbers.

The BTRC chairman said mobile operators are reluctant to maintain SIM registration process properly. As a result, criminals can use cellphones to do their acts causing deterioration of law and order.

He, however, said brand cellphone companies use a single IMEI number against one cellphone set while little known companies do not maintain it.

The BTRC chairman said though fake IMEI numbers is helping the criminals, it is not possible to control forgery as the users can buy such cellphone sets of little known companies at lower prices than those of brand companies.

If the SIM cards are registered following proper procedures by the cellphone operators there is no need to impose restriction on IMEI numbers as well as little known cellphone set companies, said BTRC Chairman Zia Ahmed adding, "We are making some new rules so that the cellphone operators are bound to maintain the SIM registration process properly."

He said a data bank of mobile operator companies will be set up under the new rules to verify identities of SIM card holders and added that national identity cards would help this process.

Additional Commissioner Mahbubur Rahman of DB said extortionists use several cellphone sets with the same IMEI number for issuing threats or demanding toll and they later alter their SIM cards to dodge law enforcers.

He mentioned that even after changing the SIM used for issuing threats, detectives earlier could identify the criminals by their IMEI numbers but recently the detectives found that 198 cellphone sets were used by a gang of extortionists using one IMEI number.

DB sources said when extortionists could understand that detectives are able to locate them by their IMEI numbers even if the SIM cards are changed, they started to use one fake IMEI number for several cellphone sets at a time.

BTRC sources said each cellphone set bears one IMEI number with 15 digits which helps locate the cellphone holder and identify the SIM card number used in the cellphone.

British Approval Board for Telecommunication (BABT) in Britain regulates IMEI numbers internationally and Bangladesh is also a member of the BABT.

DB said cellphone sets with fake IMEI numbers are available in most of the city markets and almost all the cellphone sets with fake IMEI numbers are being imported by a group of small importers.

Earlier Dhaka Metropolitan Police Commissioner AKM Shahidul Hoque told The Daily Star that top listed criminals--Dakaat Shahid, Shahadat, Monwar Hossain Manu, Khurshed and Mukul--are controlling their gangs from India while Narottam Saha alias Ashik runs his criminal acts from Dubai.