After Kolkata police officers detained CBI officials outside police commissioner Rajeev Kumar's residence, West Bengal chief minister Mamata Banejee rushed to the scene and announced that she would sit on a dharna against the "gabbar style" attitude of the central investigating agency (CBI) and the Modi-led government. The opposition parties have rallied behind Mamata and accused the central govt of destroying institution and using CBI’s as a political tool. But what’s the latest controversy about and why is West Bengal Chief Minister protesting against CBI’s move to question Kolkata Police chief? Is it an assault on federalism as is alleged by Mamata Banerjee? Watch this explainer to find answers to these questions and the way forward as the action now shifts to the Supreme Court which will now decide who’s at fault, CBI or Mamata Banerjee?