The arrest of two dummy candidates at an examination centre of Common Admission Test (CAT) 2007 in Chandigarh has prompted investigating agencies to probe the involvement of a racket in rigging the system.

“We are looking into the possibility of a larger racket operating for CAT. We are coordinating with our counterparts in Chandigarh to crack the case,” said Praveen Kumar, the superintendent of police (South 24-Parganas).

“During the physical verification of the forms, we had doubts about 40-odd application forms due to some discrepancies. So, we lodged a complaint with Thakurpukur police station,” said Dinesh Varma, the chief administrative officer of IIM Calcutta.

According to Varma, all the dubious application forms had Chandigarh as the examination centre.

On Sunday, a South 24-Parganas police team arrested two persons — Gaurav Midha, a student of NSIT Engineering College in Delhi, and Narinder Singh, an Oil India Corporation employee who had graduated from Punjab Engineering College — in Chandigarh on charges of impersonation, cheating and fraud.

The duo — caught while writing the test for others — were produced in a Chandigarh court on Monday and were denied bail.

“We are bringing them to Calcutta for further probe. Their interrogation holds the key to the case,” said an investigating officer. At this stage, the priority of the cops is to track down the candidates for whom Midha and Singh had appeared in CAT.

“As of now, it seems that the candidates are not from Bengal and there is a possibility that they are all from North India. We are working with the police from other states,” said Kumar.

Conducted by the Indian institutes of management, CAT is one of the most fiercely fought admission tests in the country. Over 2,30,00 students took the examination on Sunday for admission to the six IIMs and a host of leading B-schools that use the CAT score to screen students.

On November 14, a team from the district police — led by additional SP Praveen Kumar Tripathi — left for Chandigarh and coordinated with its counterparts there before conducting the raids on Sunday during the exams.

Chandigarh police are on the lookout for eight candidates about whom IIM Calcutta had doubts.

“These candidates failed to appear for the exam…. There could be a possibility that they were warned about the police raid in Chandigarh,” said an officer in Chandigarh.

The use of dummy candidates in CAT has come as a surprise to the IIMs, but the officials are confident about the checks and balances in the system. “We have a robust verification process and it is difficult to rig the system,” said Asish Bhattacharyya, the chairman of admissions at IIM Calcutta.

“It is not fair to question the credibility of a system just because of two arrests… The CAT panel will explore the possibility of an electronic check for applications,” he added.