The Central Board of Secondary Education on Thursday told the Delhi Police in a complaint that it received a fax on March 23, which claimed that a person who runs a coaching centre in New Delhi’s Rajinder Nagar locality was responsible for leaking its question papers, ANI reported.

The Delhi Police’s Crime Branch on Wednesday began investigating how the Class 12 economics and Class 10 mathematics question papers were leaked. The economics exam was held on Monday, while the maths exam was conducted on Wednesday, hours before the CBSE announced that it will hold the two exams again.

The Times of India reported that it received a handwritten version of the economics question paper on the day of the Class 12 exam and a handwritten version of the maths paper the day before the exam. A few students in Bihar and Abu Dhabi also claimed that they had accessed the “leaked” paper, the newspaper reported.

The police have filed two separate cases, and so far 25 people – mostly students who had access to the leaked question papers – have been questioned, NDTV reported.

“We received snapshots of the handwritten paper circulated through WhatsApp from the complainant,” an officer close to the investigation told PTI. “We are trying to find the source of these messages.”

The officer said that as WhatsApp’s messages are encrypted, it was becoming difficult to trace the source. The team has yet to question any official from the CBSE or the exam centres. “They will be questioned once the source of the messages is traced,” the officer added.

According to the first information report filed by the police, the Class 12 economics paper leak came to light when the board received an “unaddressed” envelop with four sheets containing handwritten answers to questions from the paper just as the exam began on Monday, The Indian Express reported.

On Wednesday, the Delhi Police released a statement about the cases registered and the team that has been set up to investigate them after Special Commissioner of Police (Crime) RP Upadhyay and Joint Commissioner of Police (Crime) Alok Kumar met Delhi Police Commissioner Amulya Patnaik, PTI reported.

The statement said the first case was filed in connection with the leak of the economics paper on Tuesday, while the case in the mathematics paper leak was filed on Wednesday. A Special Investigation Team, supervised by the joint commissioner (crime) and comprising two deputy commissioners of police, four assistant commissioners of police and five inspectors, will investigate the cases.

Meanwhile, the CBSE has constituted a committee to investigate the possible leak of the Class 12 accountancy question paper, India Today reported. Copies of the question paper were reportedly found posted on social media a day before the exam. “Wherever the board has found anything concrete so far, we have taken concrete actions,” the website quoted an unidentified CBSE official as saying.