The duty to impart justice in criminal cases is the responsibility of several departments. It starts with the person filling an FIR and slowly sifts to police to investigate the matter, and finally ends in the court of law where much happens between justice and the unjust methods. You with your own limitations can be part of either of departments but not the whole, and in those limitations of your responsibility you are expected to impart justice to the society. Here the article deals with the part where irregularity, illegality or defect in investigation occurs and you on other side of your case are expected to impart justice irrespective of unwelcoming circumstances, given the fact that defective investigation can leads to acquittal even of the wrong doer.
However, the impact of a defective investigation depends upon the nature of the defect. In case the investigation leaves glaring loopholes, it may lead to acquittal of the accused.
The Supreme Court has held that the power of investigative agency is large and expensive and the court have a minimum role in this regard, there are inbuilt provisions in the code to ensure that investigation of a criminal offence is conducted keeping in mind the rights of an accused to a fair process of investigation. Our criminal justice system provides safeguards of a fair trial by doing justice to all, the accused, the society and a fair chance to prove the case to the prosecution. Where the prosecution attempts to misconduct the trial on the basis of a perfunctory or designedly defective investigation, the court is to be deeply cautions and ensure that despite such an attempt, the determinative process is not subverted.
The court to ensure law in consistent with the justice system and keeping in mind irresponsibility of police in during investigation, held that not every defective investigation has been held to be a ground of acquittal. The Supreme Court explained the duty of Court in the case of defective investigation. It is settled proposition of law that even if there are some missions, contradictions and discrepancies, the entire evidence cannot be disregarded. After exercising care and caution and sifting through the evidence to separate truth from untruth, exaggeration and improvements, the court comes to a conclusion as to whether the residuary evidence is sufficient to convict the accused. The court held that undue importance should not be attached to omissions, contradictions and discrepancies which do not go to prosecution’s witness. As the mental abilities of a human being cannot be expected to be attuned to absorb all the details of the incident, minor discrepancies are bound to occur in the statement of witness. The law must be summarised to the effect that the evidence of a hostile witness cannot be discarded as a whole, and relevant parts thereof which are admissible in law, can be used by prosecution by defence.
Every irregularity or illegality in investigation is not a ground for rejection of the prosecution case and thus you can take benefit by establishing the evidence you posses beyond reasonable doubt.
 VF.K. Sasikala v. State Rep. By Superintendent, AIR 2013 SC 613
 Dayal Singh v. State of Uttaranchal, AIR 2012 SC 3046 : (2012) 8 SCC 263: (2012) 3 SCC (Cri) 838
 C. Muniappan v. State of T.N. AIR 2010 SC 3718 : (2010) 9 SCC 567
 Sorab & Anr v. The State of M.P. AIR 1972 SC 2020; State of U.P. v. M.K. Anthony, AIR 1985 SC 48; Bharwada bhogini Bhai Harji Bhai v. State of Gujarat, AIR 1983 SC 753; State of Rajasthan v, Om Prakash AIR 2007 SC2257; Prithu @ Prithi Chand & Anr v. State of Himachal Pradesh, (2009) 11 SCC 588; State of U.P. v. Santosh Kumar & Ors (2009) 9 SCC 626; State v. Saravanan & Anr 2009 SC 151
 Leela Ram v. State of Haryana, AIR 1999 SC 3717 at 3720 : (1999) 9 SCC 525