CBI sources said the defence ministry has provided them with a new set of documents related to the deal but declined to give details.
They said agency is planning to start the examination of suspects from next week.
The sources said agency had asked the Defence Ministry to provide files related to changes made in the helicopters' parameter which suited Italian company Finmeccanica and its subsidiary supplier AgustaWestland.
The agency has registered a preliminary enquiry(PE) against 11 people including former IAF chief S P Tyagi, his three cousins, European middlemen and four companies.
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All the suspects have refuted the allegations.
The sources said during PE, the agency's powers in summoning and carrying out searches are very limited and it is trying to complete the enquiry as early as possible.
In its PE, CBI mentioned allegations that in the procurement process of the helicopters, some middlemen have influenced the deal in favour of UK-based AgustaWestland.