Kochi, Sep 14 : The Cochin Shipyard where the indigenous aircraft carrier -- INS Vikrant was built and is undergoing sea trials, received a threat email again on Tuesday which warns of a bomb blast. Incidentally this is the third such threatening email received by the Shipyard in nearly four weeks. The Shipyard officials handed over the email to its security partner CISF officials, who in turn handed it to the Kochi City Police Commissioner. The police have registered a fresh case, even when the probe is going on over the previous two emails that was received, with the first one arriving on August 24 to top officials and then came another early this month, also to the shipyard officials. The Kochi police has now sought the help of the Cyber wing and the officials are confident of zeroing down on the sender. Contrary to the two previous emails, which was sent to a few top officials, this time it has been a general mail to the Shipyard. Following up on the previous two emails, the police did speak with Shipyard officials, but the probe failed to make any serious headway. The three threat emails are being viewed seriously by the officials. The officials are looking into the aspect if there was any link between an arrested Afghan national, who previously worked as a casual worker in the Shipyard, who was taken into custody from Kolkata and brought here in July. /IANS