Dear Shri Sudhir Kumar,
You may like to review your statement "Prior sanction for investigation is needed by the CBI before starting investigation against an officer of Jt Secy and equivalnet (and not below that) but this stipulation is not binding against ACB," as the reverse seems to be the position as per the provisions of Section 26.6A of the CVC Act.
Section 26.6A states as follows:
"“6A. (1) The Delhi Special Police Establishment shall notconduct any inquiry or investigation into any offence alleged tohave been committed under the Prevention of Corruption Act,1988 except with the previous approval of the Central Governmentwhere such allegation relates to—"
"(a) the employees of the Central Government of thelevel of Joint Secretary and above; and"
"(b) such officers as are appointed by the CentralGovernment in corporations established by or under anyCentral Act, Government companies, societies and localauthorities owned or controlled by that Government.".