1) Police interrogates suspects. Learns how and why crime is committed. But this is not enough to convict suspects. The statements made to police cannot be admitted in court. (Except statements about recovery of weapons, stolen items etc.)
3) Once police knows how crime is committed, he looks for Eye Witnesses to crime.
4) If there are no eye witnesses, Police looks for witnesses who have seen things happened immediately before crime and things happened after crime.
5) If whatever evidences are collected by Police, inspires "Confidence in Judge that there is no doubt that accused is the person who has committed crime," he will convict him by writing his long opinion in details.
6) His opinion and evidence recorded in his court will be examined in appeal by High Court and Supreme Court Judges. If they too feel sure that accused is the criminal, then conviction stays.
7) For routine type of murder punishment is imprisonment for whole life. If murder is done in such a way that it is "Rarest of rare crime", then death sentence can be given.
8) Lawyers help both ways. If complainant engages them, they try their best to see that accused are convicted in accordance with law. If accused engages them, they try their best to get acquittal according to law, for accused.
9) Their services are necessary because, every sentence of evidence is required to be checked and rechecked as per principles of laws laid down in books and by superior courts.
Haresh Raichura 25/3/2016