Railway Minister Mamata Banerjee today said she is not sure about the involvement of the Left-wing extremists in the attack on Jnaneswari Express in West Bengal. Her statement came a day after Home Minister P Chidambaram said Maoists are believed to be behind the attack. <br/><br/>Ms. Banerjee told reporters in New Delhi that she does not want to comment further on the issue before the investigation is over. <br/><br/>The Railways has asked for a CBI probe into the incident which claimed 149 lives. However the state government has not favoured such an idea.<br/>