Kumar, the Principal Secretary to Delhi Chief Minister Arvind Kejriwal, was examined for 12 hours, along with Intelligent Communication Systems India Limited (ICSIL) MD R S Kaushik, CBI sources said, adding that they have got important information during the interrogation.
Kumar's lawyer B S Joon said he is cooperating with the agency.
CBI has registered a case of corruption against Kumar, a 1989-batch IAS officer of Arunachal Pradesh-Goa-Mizoram and Union Territory (AGMUT) cadre, and six others for allegedly favouring a private firm in awarding Delhi Government contracts.
CBI has, however, denied the allegations.
Meanwhile, Joon said CBI is not harassing Kumar. "The allegations in the FIR are wrong. The allegations regarding tender do not stand. He was questioned regarding tenders given to ICSIL. He has been called tomorrow to be examined again regarding tenders given to Endeavour Systems Private Limited," the lawyer told reporters.