Calcutta, March 22 :     It's back to the blackboard for city cops. Calcutta Police is conducting a five-day crash course for its officers to 'improve their investigation skills' and to tutor them on presenting 'properly-framed chargesheets'. The deputy commissioner of police, detective department, Narayan Ghosh, said about 400 officers from various police stations and the detective department are busy attending classes at the Lalbazar police headquarters. 'Classes are needed for improving their knowledge of investigation, as we have seen that, sometimes, investigators fail to collect evidence on the spot due to lack of knowledge,' explained Ghosh. Senior forensic experts - director of Forensic Science Laboratory N. K. Nag and Dr Apurba Nandi of R G Kar Medical College and Hospital - and senior IPS officers - ACP Sujoy Chakrabory; ACP (II) S. I. S Ahmed; and ACP (III) D. Sarengi - are conducting classes on subjects like collection of evidence, investigation of murder, dacoity, cheating, fraud and kidnapping for ransom cases. Special emphasis is being laid on the need to improve techniques and skills of handling kidnapping cases as abductions are on the rise in the city. Sub-inspectors attending the course are being taught the basics of forensic science as well. The cops are also being tutored by the chief public prosecutor of the city sessions court to know how to frame proper chargesheets and to handle cases at the trial stage. 'The chief public prosecutor is explaining how to file a fool-proof chargesheet to ensure conviction,' said Ghosh. This comes in the wake of several cases having falling through in court due to faulty charge-sheets.