Differences between Investigation under Section 156 and Section 202 of Code of Criminal Procedure are as follows:
The various steps adopted for investigation under Section 156 Cr. P.C. have been elaborated in Chapter XII of the Code. Such investigation would start with making the entry in a book to be kept by the officer-in-charge of a police station, of the substance of the information relating to the commission of a cognizable offence.
The investigation started thereafter can end up only with the report filed by the police as indicated in Section 173, of Cr. P.C. The investigation contemplated in that Chapter (i.e., Chapter XII) can be commenced by the police even without the order of a Magistrate.
But that does not mean that when a Magistrate orders an investigation under Section 156 (3), it would be a different kind of investigation. Such investigation must also end up only with the report contemplated in Section 173 of the Code.
But the significant point to be noted is that when a Magistrate orders investigation under Chapter XII, he does so before he takes cognizance of the offence. But if he propose to take the cognizance of the offence, then he need not order any such investigation under Chapter XII but instead follow the procedure envisaged in Chapter XV of the Code. A reading of Section 202 (1) makes the position clear that the investigation referred to therein is of limited nature. The Magistrate can direct such investigation be made either by a, police officer or by any other person. Such investigations only for helping the Magistrate to decide whether or not there is sufficient ground for him to proceed further in the case.