The CBI in a number of high- profile and politically sensitive cases has not been able to cross the hurdle of judicial scrutiny as was evident in the 2G spectrum allocation matters.

The investigating agency, which was once termed as a "caged parrot" by the Supreme Court, had been left red-faced by the courts in many such cases, putting a question mark over the probe conducted by it.

From the alleged corruption cases in the 2G spectrum allocation to criminal matters such as the sensational Aarushi murder case, the probe by the Central Bureau of Investigation (CBI) has come under sharp criticism not only from the trial courts and high courts but also from the apex court.

The 2G spectrum cases, which had rocked the Manmohan Singh-led UPA-II government, led to the filing of charge sheets by the CBI in four different matters along with documents running into lakhs of pages but the agency could not secure even a single conviction.

In two cases dealt with by the special 2G court -- the Aircel-Maxis deal and the additional spectrum allocation matter -- the accused were discharged while in the main case involving former telecom minister A Raja and others, all the accused were yesterday acquitted.

Special CBI Judge O P Saini, who adjudicated all the 2G matters, had also let off the promoters of Essar Group and Loop Telecom.

The theory of the CBI in the murder case of Aarushi and domestic help Hemraj had come under sharp criticism in October from the Allahabad High Court which had termed it as "impossible hypothesis" and "patently absurd".

The high court had acquitted Aarushi’s parents, dentists Nupur and Rajesh Talwar, holding that the prosecution had "miserably failed" to prove that the Talwars had destroyed material evidence. The dentist couple were convicted by a Ghaziabad court in 2013 and sentenced to life imprisonment.

The CBI’s investigation in the politically sensitive Bofors payoff case was also unable to withstand judicial scrutiny with the Delhi High Court on May 31, 2005, quashing all the charges against the Hinduja brothers -- Srichand, Gopichand and Prakashchand -- and the Bofors company.

The high court had also castigated the CBI over its handling of the Bofors case, saying it had cost the exchequer about Rs 250 crore.

The CBI’s Multi-Disciplinary Monitoring Agency probe into the larger conspiracy aspect in the assassination case of former prime minister Rajiv Gandhi has recently come under the radar of the top court.

In scathing remarks, the apex court had observed that the investigation does not appear to have achieved "much headway" and could be "endless".

In the coal scam, the CBI was time and again caught on the wrong foot by the apex court and the special trial court over its investigation.

The Supreme Court had in May this year slammed the CBI for "failing to live up to its reputation" in a fodder scam case involving RJD chief Lalu Prasad, saying there was "intolerable lethargy" in filing an appeal.

The CBI’s case relating to alleged illegal mining in Bellary in which the agency had charge sheet former Karnataka chief minister B S Yeddyurappa and others, also fell flat with the trial court discharging all the accused.