Death threat letter sent to Mamata Banerjee's chief advisor - Alapan Bandyopadhyay, addressed to his wife.

An unknown death threat was allegedly given to former West Bengal Chief Secretary Alapan Bandyopadhyay through a letter addressed to his wife.

A letter addressed to Bandyopadhyay's wife Sonali Chakraborty, Vice-Chancellor of Calcutta University, said: "Your husband will be killed, no body can save the life of your husband."

Kolkata police in an official statement said, "Over the complaint of Sonali Chakraborty Bandopadhyay, Hare Street PS lodged FIR, dated October 26, under section 170/419/500/506 of Indian Penal Code against unknown people".

Alapan is currently serving as the chief advisor to West Bengal Chief Minister Mamata Banerjee.

Further investigation is underway.