He also said that CBI is "vigorously" pursuing the matter.
"My commitment to Parliament stands. I do feel somebody has taken money. The enquiry is at a crucial stage. We will not show mercy to anybody and will take action, however, powerful he may be," he told reporters here when he was asked about the AgustaWestland deal.
"Please wait for some more time. There is no doubt very strict action would be taken against those involved," he said.
CBI, lead probe agency in the case, had received some more crucial documents from the Defence Ministry and Italy in connection with the Rs 3,600-crore deal. The documents, carrying details of money trail, have been shared with the Enforcement Directorate.
The agency has already registered a Preliminary Enquiry (PE) against 11 people, including former IAF chief S P Tyagi, his three cousins, European middlemen and four companies.
All the suspects have refuted the allegations.
In its PE, registered to probe alleged kickbacks in the 12 AW-101 VVIP helicopters from AgustaWestland deal, CBI is looking into the role of some middlemen suspected to have influenced the deal in favour of the Italian company.
The agency suspects that a portion of Rs 362 crore bribe was allegedly routed to Indian nationals, through Tunisia and Mauritius, camouflaged as payments for engineering contracts to Chandigarh-based-IDS Infotech and Aeromatrix. Both companies had denied involvement in the bribery scandal.
The CBI is likely to send judicial requests to UK, Italy, Mauritius and Tunisia seeking information about financial transactions carried out by accused in the deal.