Has CBI of India any credibility?

CBI's failure to catch the culprits in Aarushi murder case and just showing suscpicion on the parents without esatablishing the motive despite having subjected the parents to lie detection, and all sorts of tests places a question mark on CBI's credibility. Can anyone cite a single instance of CBI's success in any case? Even their website was hacked by Pakistani boys and remained offline for days together. In Aaarushi murder case, no one looked into the possibility of the intension of the murderer to kill Hemraj and that Aarushi was killed as she might have been the witness. There is a possibility that Hemraj may have some problem with people in his native place and there was the need to look into this possibility and check if there were return rail tickets booked by someone from Nepal to Talwar's hometown and back during those days. During early media reports, I recall having heard that Hemraj had the fear of being killed by someone which he had told to some social worker and sought her help, but there is no investigation in that direction. The present strategy of CBI seems to get an end to this difficult job by charging the parents who finally will prove that they are innocent and the case will close. But who will be responsible for the hardship of the parents and failure of CBI to nab the culprits?