@Sh. Assumi,
The reinvestigation necessiates when the trial judge comes to know that the accused is the real culprit but cannot convict him as the I.O. due to inefficiency or malafide intentions has left certain aspects, which required investigation and the outcome of the reinvestigation, according to judge's perception, proves the guilt of the accused beyond reasonable doubt. If the investigation is a faulty one, in the appeal also, justice cannot be delivered, as reappreciation of same facts cannot change the mind of appellate court. Of course, the reinvestigation can be ordered only before taking the statements of accused under S.313. Kindly refer Section 319, which says during the trial, if the court comes to the opinion that some other person is also co-accused, it would call him and conduct trial afresh. I am citing this section only for the purpose, that the trial court has got the power even during the trial for reinvestigation. These are only my opinions. Not based on any precedents.
@ Sh. Jaiswal,
You should not wonder if the trial court judgment may be turned down by the appellate court. There is a scope for reappreciation of evidence and hence decisions may change in the appeals. That is why precisely, the scope for appeal is provided.