The investigation into the recovery of firecrackers from a Kingfisher aircraft that arrived here from Bangalore on Sunday is centred on the loaders engaged by the private agency that handles the cargo of the airline in Thiruvananthapuram.

The loaders, especially those who were on duty then, are under the surveillance of the city police. The Bangalore police have ruled out chances of keeping the firecrackers in the rear cargo hold area of the ATR-72 aircraft in the Bangalore international airport.

The police are keeping a close watch on six loaders who were on duty and the other five on the rolls of the agency. Sources said the police carried out searches on their houses as they were the only ones who had access to the aircraft besides the designated airline staff.

The fact that the firecrackers were wrapped in a Malayalam newspaper and SSLC question papers support the theory that it might have been planted in Thiruvananthapuram.

Police sources say they are yet to come to any conclusion on how the firecrackers were placed in the cargo hold area of the aircraft.

A team led by City Police Commissioner, M.R. AjithKumar that had gone to Bangalore on Sunday to probe the incident returned on Monday.

Sources say the team, comprising Assistant Commissioners K.C. Sasikumar and K.E. Baiju, questioned the airline staff and loaders engaged by the airline in Bangalore. The team watched the CCTV footages at the Bangalore airport and took statements of the passengers who were on the flight.

A three-member team of the Bangalore police arrived here as part of the investigation into the incident. The team reportedly questioned the airline staff and the loaders here. Though the quantity of the explosives, weighing 10-15 gm, is not powerful enough to blow up the aircraft or cause any other damage, the incident has been labelled by the Civil Aviation Ministry as a major security lapse. The chemical analysis of the firecracker has revealed that it contained sulphur, aluminium powder and potassium chlorate.

Meanwhile, security has been stepped up in the airport. A meeting presided over by airport director V.N. Chandran on Monday reviewed the security arrangements. All airlines and user agencies have been asked to be vigilant.