evidence of a witness is his evidence in court but when the accused person is not previously known to the witness concerned then identification of the accused by the witness soon after the former's arrest is of vital importance because it furnishes to the investigating agency an assurance that the investigation is proceeding on right lines in addition to furnishing corroboration of the evidence to be given by the witness later in court at the trial. From this point of view it is a matter of great importance both for the investigating agency and for the accused and a fortiori for the proper administration of justice that such identification is held without avoidable and unreasonable delay after the arrest of the accused and that all the necessary precautions and safeguards are effectively takenso that the investigation proceeds on correct lines for punishing the real culprit. It would, in addition, be fair to the witness concerned who was a stranger to the accused because in that event the chances of his memory fading are reduced and he is required to identify the alleged culprit at the earliest possible opportunity after the occurrence. It is thus and thus alone that justice and fairplay can be assured both to the accused and to the prosecution. The identification during police investigation, it may be recalled, is not substantive evidence in law and it can only be used for corroborating or contradicting evidence of the witness concerned as given in court. The identification proceedings, therefore, must be so conducted that evidence with regard to them when given at the trial, enables the court safely to form appropriate judicial opinion about its evidentiary value for the purpose of corroborating or contradicting the statement in court of the identifying witness.”