Death threat in Airlines from a passenger who illegally occupied seat

Dear sir, yesterday I was travelling on Indigo airlines, I was given seat 12F passenger refused to give the seat even after air hostess and ground staff requested, and started hurling insults and threats. Fellow passengers tried to intervene and I had to move even after I was paid for the seat. What action can law take against passenger who is occupying Paid seat and hurling abusive language, death threats? Entire incident is caught on tape, I will share all the details. I want indigo to intervene in future atleast. How can we file case against such persons? What should a passenger do in such helpless situation?