Kolkata (West Bengal) [India], August 28 (ANI): Authorities have tightened security in Kolkata in the wake of the 12-hour ‘Bengal Bandh’ call by the BJP in protest against the alleged police crackdown during the ‘Nabanna Abhijan’ protest rally in the state capital on Tuesday. The murder and alleged sexual assault of a female trainee doctor on August 9 at RG Kar Medical College and Hospital on August 9 caused national outrage and many rallies have been held in different states of the country. Dendup Sherpa, Additional Superintendent of Police (SP), Uttar Dinajpur, a district in West Bengal, tol…