In Ankush Maruti Shinde The Supreme Court expressed its displeasure against the police for the manner in which it had investigated an offence in which several people were murdered and a woman raped in which, the accused persons, who were members of a nomadic tribe were falsely implicated while, the actual perpetrators of the crime who were identified by the witness's from the register at the police station, where never proceeded or investigated into. Underscoring the importance of a fair investigation, The Supreme Court held "It has to be uppermost kept in mind that impartial and truthful investigation is imperative. It is judiciously acknowledged that fair trial includes fair investigation as envisaged by Articles 20 and 21 of the Constitution of India. The role of the police is to be one for protection of life, liberty and property of citizens, that investigation of offences being one of its foremost duties. That the aim of investigation is ultimately to search for truth and to bring the offender to book". In the same judgment, The Supreme Court, relying upon an earlier judgment passed in V.K. Sasikala Vs. State - (2012) 9 SCC 771, Highlighted the importance of the police in examining the documents that maybe in support of the accused and held in the following words "As observed by this Court in V.K. Sasikala v. State [V.K. Sasikala v. State, (2012) 9 SCC 771 : (2013) 1 SCC (Cri) 1010] , though it is only such reports which support the prosecution case that are required to be forwarded to the Court under Section 173(5), in every situation where some of the seized papers and the documents do not support the prosecution case and, on the contrary, support the accused, a duty is cast on the investigating officer to evaluate the two sets of documents and materials collected and, if required, to exonerate the accused at that stage itself"[Para No.21]
In Babubhai Vs. State of Gujarat, The Supreme Court examined a case arising from a fight between two groups in which three people died. The police are alleged to have examined the case only from the standpoint of one, completely ignoring the defence of the other. Emphasising on the importance of a fair investigation, the Supreme Court held "The investigation into a criminal offence must be free from objectionable features or infirmities which may legitimately lead to a grievance on the part of the accused that investigation was unfair and carried out with an ulterior motive. It is also the duty of the investigating officer to conduct the investigation avoiding any kind of mischief and harassment to any of the accused. The investigating officer should be fair and conscious so as to rule out any possibility of fabrication of evidence and his impartial conduct must dispel any suspicion as to its genuineness. The investigating officer "is not merely to bolster up a prosecution case with such evidence as may enable the court to record a conviction but to bring out the real unvarnished truth". (Vide R.P. Kapur v. State of Punjab [AIR 1960 SC 866 : 1960 Cri LJ 1239] , Jamuna Chaudhary v. State of Bihar [(1974) 3 SCC 774 : 1974 SCC (Cri) 250 : AIR 1974 SC 1822] , SCC at p. 780, para 11 and Mahmood v. State of U.P. [(1976) 1 SCC 542 : 1976 SCC (Cri) 72 : AIR 1976 SC 69] )". Further, in the same judgement Supreme Court held "Not only fair trial but fair investigation is also part of constitutional rights guaranteed under Articles 20 and 21 of the Constitution of India. Therefore, investigation must be fair, transparent and judicious as it is the minimum requirement of rule of law. The investigating agency cannot be permitted to conduct an investigation in a tainted and biased manner. Where non-interference of the court would ultimately result in failure of justice, the court must interfere. In such a situation, it may be in the interest of justice that independent agency chosen by the High Court makes a fresh investigation"[Para No.22]
Thus, fair investigation by the police is an imperative facet inhering in Article 21. It is not an option but a constitutional mandate on the police that when it investigates, it must be done, not from the standpoint of the prosecution alone, but also from the point of view of the accused. It has to consider the defence put forth by the accused which if investigated fairly, may exonerate him. The purpose of investigation is not to secure a conviction of the accused but to unearth the truth relating to the commission of an offence. A partisan investigation is a defective investigation which puts a question mark on the sanctity of the proceedings against the accused. If after taking the defence of the accused into consideration the police is of the view that the accused is not the person who committed the offence, in such a situation he is to be exonerated and the case against him, closed. In the present case, the investigation was initially biased and one-sided. There was even reluctance on the part of the police to accept documents from the accused. Even after the police had received the prurient photographs of the deceased, it never carried out any investigation to examine the motive of the deceased to commit suicide and whether the reason put forth by the Petitioner was plausible. The police have merely taken the material given by the Petitioner and made the same a part of the chargesheet without conducting any investigation into the defence of the Petitioner. The police have merely recorded the statement of the immediate relations of the deceased and filed the chargesheet against the Petitioner. No investigation was conducted to a certain the veracity of the allegations against the Petitioner.[Para No.23]
In other words 
