Gopal Krishna Madhav was posted in Manish Sisodia's office since 2015, officials said.
The CBI on Friday carried out searches at the premises of an IAS officer in connection with the arrest of Gopal Krishna Madhav, officer on special duty to Delhi's Deputy Chief Minister Manish Sisodia, officials said.
They said Gopal Krishna Madhav was arrested on Thursday evening on the basis of information provided by a middleman, arrested on Wednesday, who allegedly collected bribes from transporters on his behalf.
During questioning, Gopal Krishna Madhav has alleged the involvement of the IAS officer following which the agency carried out searches at the latter's premises, the officials said.
The arrest of Gopal Krishna Madhav was made by the agency in an operation on Thursday evening after middleman Dheeraj Gupta, nabbed on February 5, claimed that he was collecting money on behalf of the former.
The arrests come ahead of the crucial Delhi Assembly elections. Sources said the agency has not found Manish Sisodia's involvement in the case so far.
"CBI has arrested Dheeraj Gupta, a private person, who is a resident of Delhi and Gopal Krishna Madhav, Goods and Services Tax Officer in Trade and Taxes Department of Government of NCT Delhi, who is also the OSD to Deputy CM of Delhi, in a bribery case of Rs. 2.26 lakh," a CBI spokesperson said.
During questioning, Gupta claimed that he was collecting the bribe for Gopal Krishna Madhav, a Delhi Andaman and Nicobar Island Civil Service (DANICS) cadre officer in the trade and tax department, officials said.
"It was alleged that the private person (Gupta) was acting as a middleman on behalf of some GST department officers, including for the public servant (Madhav), for collecting illegal gratification from transporters for not charging GST from them," the spokesperson said.
Gopal Krishna Madhav was immediately taken to the headquarters where he was questioned in detail by CBI officers, officials said.
Gupta has been sent to judicial custody by a special court while Gopal Krishna Madhav will be produced before the court on Friday, they said.
Gopal Krishna Madhav was posted in Manish Sisodia's office since 2015, they said.
Reacting to the development, Sisodia tweeted, "I have come to know that the CBI has arrested a GST inspector while taking bribe. This officer was posted as OSD in my office too. CBI should ensure strictest punishment for him. I have got several such officers arrested during last five years."