NEW DELHI: In a sophisticated operation, the CBI scoured through 40-feet of sand at the seabed in a creek near Thane to recover a gun which might be the clinching evidence in the killing of rationalists including Narendra Dabholkar , officials said on Thursday.

The agency relied on the expertise of a Dubai-based company — Envitech Marine Consultants — which used hi-tech Norwegian equipment and Ukrainian divers to detect the gun in a 40-feet thick layer of sand on the seabed in an operation that cost Rs 7.5 crore, to be shared by the governments of Karnataka and Maharashtra.

Rationalists Dabholkar, Gauri Lankesh , M M Kalburgi and Govind Pansare were shot dead in similar fashion allegedly by right-wing extremists, they said.

The agency is probing the killing of Dabholkar who was allegedly shot dead on August 20, 2013 in Pune by members of Sanatan Sanstha, a right-wing extremist group, whereas the Karnataka police is investigating the murders of Kalburgi, Lankesh and Pansare, they said.

"The weapon will be sent for ballistic tests which will give a clear picture whether it was used in Dabholkar's murder or any other case. Meanwhile, the search operation is still going on to locate other weapons used in similar murders," an official said.

Initial reports indicate the killers' modus operandi being similar in all the four cases and that the killings may have some common actors, they said.

Alleged shooter in the Dabholkar case, Sharad Kalaskar, has claimed to have thrown four weapons used in the murders in the creek on the directions of a Sanatan Sanstha member, the agency had said.

Finding a gun in the huge creek area meant managing through tides, looking into dirty water, rocks and sand in the seabed as the suspected weapon could have been at any depth of sand, officials said.

After the interrogation of suspects, the agency narrowed the area where they had thrown their respective weapons from the bridge.

Senior officials gave a go-ahead for using expertise of Envitech which brought in equipment from Norway and expert deep sea divers from Ukraine to successfully find a weapon which might have been used in Dabholkar's killing.

The sonar (sound navigation and ranging) technology helped the agency locate metal objects through depths of the seabed which was followed by a delicate layer by layer removal of sand using a crane arm fixed on a floating platform, they said, adding that it was ensured that the crane only removed sand without touching the weapon as it could have damaged the potential evidence.

Later, expert divers from Ukraine were sent to bring out the weapon with careful handling, the officials said.

The operation footed a bill of Rs 7.5 crore to be shared by the governments of Karnataka and Maharashtra, they said.

