New Delhi, Feb 10 (IANS): The arrest of Gopal Krishna Madhav, an OSD to Delhi Deputy Chief Minister Manish Sisodia, and a middleman by the CBI helped bust a "gang of middlemen" active in the GST Department, an official source said on Monday.

The CBI source said: "During questioning of accused GST Officer Madhav and middleman Dheeraj Gupta, we came to know about the gang active in the Tax Department, following which the agency directed a number of other Goods and Services Tax GST) officers and an IAS officer to join the probe."

The CBI had arrested Gupta, a resident of Delhi, on Wednesday in the bribery case involving Rs 2.26 lakh. Gupta allegedly told investigators that he was collecting the bribe for Madhav, a Delhi Andaman and Nicobar Island Civil Service cadre officer.

Gupta was allegedly collecting bribes from transporters on the officer's behalf.

Madhav, arrested on Thursday, in turn pointed to senior IAS officer Udit Prakash Rai's involvement, following which the Central Bureau of Investigation searched the latter's residence and office.

The source said the central agency had not found Sisodia's involvement in the case so far.