CBI sources said the paper was allegedly procured by Hissar-based mastermind Surinder Kumar, who is on the run, and he sent the scanned copy of the paper to his associates through 'Whats App'.
In addition to exchanging messages, the mobile application can be used for sending multi-media products including the pictures, voice messages and songs to users.
The sources said the gang-members, who were sitting outside the examination centre in the car here, solved the paper in batches of five questions each and communicated the answer keys through hidden bluetooth devices to candidates who were writing the papers.
For providing these services, Kumar allegedly charged Rs 20 lakh from each of the aspirant. The agency has managed to nab six aspirants, who include an Income Tax inspector Amit Khatri posted at Mumbai, while it is still searching for other aspirants who might have used the gang's services.
The sources said Khatri was apprehended with two high-end phones, a tablet and Armani shades besides cash.
They said he was allegedly trying to move to Delhi zone of the Income Tax department and used the services of the gang for clearing the examination.
The agency has so far arrestedn 13 persons including six students and seven gang members, who were produced before a special court here seeking custody.
The sources said a Delhi Police Sub-inspector posted at Sarai Rohila, Praveen Mann, a private person Vikram Singh Mann and Mukesh Kumar Mann have been sent to CBI custody till October 6. The others arrested, including Manoj Kumar and Rajnish Mann, have been sent to judicial custody.
"It was alleged that the members of the said group adopted a unique modus operandi and got question paper leaked in criminal conspiracy with unnamed govt officials. Thereafter, the accused got the same solved with the assistance of experts," CBI spokesperson had said.
The official said when the examination was being held on September 29, the gang members communicated the answer keys to the aspiring candidates in the examination hall through their mobile phones and other such devices in return for money.
"The aspiring candidates, while working in close nexus with said group, had carried the mobile sets and other such devices in the examination hall while concealing the same in their clothing," the official said.