After failing to get any response from the Centre, thirty members of Netaji Subhas Chandra Bose's family have sought West Bengal Chief Minister Mamata Banerjee’s intervention in revealing the mystery surrounding the disappearance of the nationalist leader.

Demanding declassification of all secret records about the freedom fighter, who was last seen at Bangkok Airport on 17 August 1945, the kin have written a letter to her saying that she should "raise this demand with Prime Minister on behalf of Netaji's countless admirers all over the world".

"We are approaching the chief minister because we think that it will be most appropriate that this demand for declassification should be made by a fervent admirer of Netaji Subhas, Chief Minister of West Bengal," reads the letter released to the media today.

Chandra Kumar Bose, a grandnephew of Subhas Chandra Bose, said they are waiting for the chief minister to respond to their campaign. They want Banerjee to "persuade the Centre to declassify all secret material and files being maintained by various ministries and departments of the government, including the intelligence agencies".

"There are so many theories floating around. Someone says he died in a plane crash in Taiwan, others say he came back to India in the disguise of 'Gumnami Baba' or he died in Russia. But there is no evidence to prove what happened to him. We want to know the truth," Chandra told PTI.

In the letter, the family members say that even after over six decades the country is still mystified by the disappearance of Bose. They have also reiterated support of the finding of Justice Mukherjee Commission of Inquiry in 2006 that "the story of Netaji's death in a plane crash in 1945 was a hoax".

"The government continues to hold back a large number of top secret or secret documents whose disclosure could decisively bring an end to the controversy. It is thus imperative in the national interest to release all information related to Netaji," the letter demands.

When under house arrest by the British, Netaji had escaped from India in 1941 to seek international support for India's freedom struggle. After organising Indian National Army with Japanese help he went missing in 1945, giving birth to India's most debated and puzzling mystery.

In a disclosure under RTI appeal made by 'Mission Netaji', a Delhi-based research trust, Prime Minister's Office had earlier said that it was holding 33 secret files concerning Netaji.

It had declined to divulge their contents saying it could affect India's sovereignty and relations with foreign nations.