By A Staff Reporter : A day after Sidhu Moosewala, a Punjabi singer and Congress leader, was shot dead in Mansa district, his father Balkaur Singh wrote a letter to Punjab Chief Minister Bhagwant Mann on Monday.In the letter, he demanded an investigation by the Central Bureau of Investigation (CBI) and the NIA. In the letter, Sidhu's father informed the Chief Minister that the case of his son's death should be investigated by a sitting High Court judge. He demanded that those responsible for ordering the withdrawal of his son's security be held accountable.