Delhi Police Sub-Inspector Sanjay Gupta, who was the investigating officer in the CBSE Pre-Medical Test question paper leak case, has admitted to extorting money from the father of the main accused, CBI sources claimed on Monday.

After intense rounds of interrogation during the last three days, Gupta reportedly broke down saying he was facing a severe financial crunch after making a huge investment in purchasing a house in Dwaraka in southwest Delhi and had extorted money from Om Prakash Verma, the father of the main accused.

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Initially reluctant to co-operate with the CBI, the Crime Branch cop was cornered with a tapped conversation that he had with Verma, the sources said.

Delhi Police constable Umeed Singh, who was also arrested by the CBI last week along with Gupta, had reportedly told the sleuths that he had threatened the Vermas on Gupta's orders.

The CBI has also started scrutinising 45 files, seized from Gupta's office during raids, and were probing whether investigations in other cases were carried out thoroughly.

Meanwhile, a search is on to nab Gupta's colleague, Rakesh Kumar, who had allegedly escorted Verma to the arrested Sub-Inspector's car with the extorted money.