NEW DELHI: The Central Bureau of Investigation ( CBI ) is on an overdrive under its acting director Rakesh Asthana with big arrests effected under his watch in the last 25 days in long-pending cases, bringing the heat upon the political rivals of the ruling establishment.Former Air Force Chief SP Tyagi and two other accused have got bail after being arrested by CBI in the AgustaWestland case within a week of Asthana becoming the acting chief. Questions are being raised why such high-profile arrests, including those of Trinamool Congress MPs, are being effected by the agency which usually desists from arrests.“Non-cooperation with probe is not the only ground to arrest someone. An accused is arrested to confront him with the evidence collected – when the material turns substantial. This is done under custodial interrogation. That is why Tyagi was arrested at the stage he was. There is strong evidence that he was paid a big bribe,” a senior CBI official told ET.It has also been questioned why CBI did not act for three years when Tyagi was appearing before them after the FIR was lodged in 2013. “You cannot accuse us of inaction as well as now for action,” the CBI official said.Asthana is said to have given the green-signal to expand the probe to the politicians too, in what could rile the Congress party as initials of some of its leaders are said to feature in a diary forwarded to CBI by Italian courts.“We will corroborate the same before summoning politicians for questioning,” a CBI official said. In an unprecedented step, CBI has also challenged the bail given to Tyagi before the High Court – pleading him to be kept in jail and away from other suspects till the CBI files a chargesheet.“The first charge-sheet in Agusta case will be filed next month. The amount of bribe established by us is euros 52 m – 30 m through Christian Michel and euros 22 million through Guido Haschke – to benefiaries,” the CBI official said.The same grounds are being cited for arrest of Trinamool Congress MPs Sudip Bandopadhyaya and Tapal Pal in the last one week in a chit fund case of Rs 17,000 cr. “The case is pending since 2014. A first chargesheet has been filed and we are investigating the larger conspiracy and the money trail. Hence, the arrests of MPs now after we got evidence against them. More arrests are on cards,” a CBI official said.CBI has also received the reference from Haryana government regarding the National Herald case against former Haryana CM Bhupinder Singh Hooda . Seven cases against AAP government in Delhi are under CBI probe too.On December 9, a week after Asthana took over, CBI also filed a chargesheet against former Union ministers from DMK, Dayanidhi Maran and Kalanithi Maran, in the illegal phone exchange case which had been pending since 2013.Asthana, a Gujarat-cadre IPS officer perceived to be close to the ruling establishment, “has been sandwiched in a political fight”, an official close to him reasoned. “He is not even eligible to become the CBI Director as he is from the 1984 batch of IPS which is not yet empaneled. Ordinarily, CBI director is picked from the four senior-most batches – in this case from 1979 to 1983 batches. Prashant Bhushan has filed a plea before SC challenging Asthana’s appointment.The Centre is still to call a meeting of the selection committee to select the next director. The joke in CBI is Asthana may have already set the work agenda for the next director with the probes fast-tracked by him.