When Police investigates 498a cases. The Statements of all the witnesses are important and it gets recorded under 161 CrPC and becomes part of chargesheet.
CrPC 161 says:
Examination of witnesses by police.(1) Any police officer making an investigation under this Chapter, or any police officer not below such rank as the State Government may, by general or special order, prescribe in this behalf, acting on the requisition of such officer, may examine orally any person supposed to be acquainted with the facts and circumstances of the case.(2) Such person shall be bound to answer truly all questions relating to such case put to him by such officer, other than questions the answers to which would have a tendency to expose him to a criminal charge or to a penalty or forfeiture.(3) The police officer may reduce into writing any statement made to him in the course of an examination under this section; and if he does so, he shall make a separate and true record of the statement of each such person whose statement he records.
Now the importance of 161 CrPC is that it can be used for contradiction. When police witnesses come too the court for Statements under Oath.
Now there are two ways to show contradiction
The portion of statement which is about to use for contradiction first brought to the notice of witness, and should be questioned about it. If the witness admits that he made said statements before police then no further proof is needed. But if witness denies that he made confronting statements that he did not make before police then, comes the role of contradiction, court is bound to note the said statements and give exhibit number. By that process contradiction merely brought on record but those are subject to proof. It is said to be proved if investigating officer who recorded statement is confronted with the said statement asking whether witness stated about passage beofre him or not. If he gives affirmative answer, then the said contradiction said to be proved. In a case reported in AIR 1958 Bom 225, Syyed Husan Vs State, their lordship held that the correct way and the proper way of proving a contradiction or omission is to ask the investigating officer (SI) about it in his evidence, as to whether a certain statement was made before him by a witness. If such a procedure is not adopted, it cannot be said that there was proof that in fact the statement concerned was not made by the witness. It is for the trial judge to decide in each case, after comparing the part or parts of the statement recordedby the police with that made in the witness box, to give a ruling having regard to the aforesaid principles whether the recital intended to be used for contradiction satisfies the requirements of law.