Section 1 of the Code of Criminal Procedure, 1973 provides for Short title, extent and commencement which reads thus:
1. Short title extent and commencement.
(1) This Act may be called the Code of Criminal Procedure, 1973.
(2) It extends to the whole of India except the State of Jammu and Kashmir:
Provided that the provisions of this Code, other than those relating to Chapters VIII, X and XI thereof, shall not apply-
(a) to the State of Nagaland,
(b) to the tribal areas,
but the concerned State Government may, by notification, apply such provisions or any of them to the whole or part of the State of Nagaland or such tribal areas, as the case may be, with such supplemental, incidental or consequential modifications, as may be specified in the notification.
Explanation. – In this section, “tribal areas” means the territories which immediately before the 21st day of January, 1972, were included in the tribal areas of Assam, as referred to in paragraph 20 of the Sixth Schedule to the Constitution, other than those within the local limits of the municipality of Shillong.
(3) It shall come into force on the 1st day of April, 1974.
Neither Criminal Procedure Code 1973 nor Indian Penal Code 1860 applies to the State of Jammu and Kashmir. The State got different Cr.P.C. known as Jammu and Kashmir Code of Criminal Procedure. Similarly instead of Indian Penal Code 1860 it has Ranbir Penal Code. Goyal Agencies Vs. State of Uttar Pradesh [Allahabad High Court, 31 January, 2008]
Members of the CBI have to investigate as if they are the members of the Police force of the State of Nagaland in accordance with the notifications or the Rules applicable in the State of Nagaland. However, the principles of the Code of Criminal Procedure would be applicable. The CBI has only limited job to be performed i.e. the investigation. Powers and jurisdiction have been conferred on the members of the DSPE only for the purpose of investigation. [Surinder Singh Ahluwalia v Delhi Special Police, 1991 CriLJ 2583 : ILR 1991 Del. 228]
The Code of Criminal Procedure is not applicable in Nagaland in view of the Rules for the Administration of Justice and Appeals in Naga Hills District, 1937. Only spirit of the Code is applicable. [Mowu v. Superintendent, Special Jail Nowgong, Assam, (1971) 3 SCC 936]
The Criminal Procedure Code is not applicable by reason of Sixth Schedule to the Constitution in this area. [V.L. Rohlua vs. Deputy Commissioner, Aijal,. District Mizo (1970) 2 SCC 908]
Only the spirit of the Criminal Procedure Code applies. [State of Nagaland v. Rattan Singh,  3 S.C.R. 830]