What exactly is CBI doing ?

If we look at the past, we all know how honest had all our politicians and bureaucrats been. The Central Bureo of Investigation was primarily created with following divisions:

• Anti Corruption Division: Cases of corruption and fraud committed by public servants of all Central Govt. Departments, Central Public Sector Undertakings and Central Financial Institutions.

• Economic Crimes Division: Deals with cases including bank frauds, financial frauds, Import Export & Foreign Exchange violations, large-scale smuggling of narcotics, antiques, cultural property and smuggling of other contraband items etc.

• Special Crimes Division: Deals with cases such as cases of terrorism, bomb blasts, sensational homicides, kidnapping for ransom and crimes committed by the mafia/the underworld.                      (Source:  Wikipedia)

Now if we analyze their work particularly in anti corruption,  I cant remember any of the politician or a top notch bureaucrat being nabbed by CBI. The Raja's 2G scam was discovered by central Vigilence Unit so was the case of Hasan Ali where Supreme Court has to intervene when it found CBI doing nothing. This is the story with almost all the prominent cases.

Even now that the CBI is investigating  the 2 G scam, the charge sheet filed by CBI is kind of soft towards Raja. I really dont understand what exactly are they doing ? Is there some genuine conflict of interest where all the posting and promotions of CBI are being done by the influential politicians and bureaucrats and they just cant do anything about them ?