The Enforcement Directorate is probing the money trail in connection with the case.

The Central Bureau of Investigation on Wednesday summoned Mathew Samuel, the whistleblower in the Narada sting operation case, to appear before it for questioning on June 24.

Mr Samuel, who is the editor and managing director of Narada news portal had, in 2016, broadcast a sting video on his news portal. The video came to the fore just before the commencement of the state Assembly elections.

In the sting video, a number of Trinamool Congress leaders, including MPs and ministers, were allegedly seen taking money on camera.

The Enforcement Directorate is probing the money trail in connection with the case.

Several legislators and TMC leaders have been quizzed by the probe agencies so far.

On June 2 this year, ED had issued summons to Shreya Pandey, daughter of State Consumer Affairs Minister Sadhan Pandey, and estranged wife of former Kolkata Mayor Sovan Chatterjee -- Ratna Chatterjee -- for questioning in the case.