What is the real story behind movie Badlapur?

In a Reuters interview, the director Sriram Raghavan was asked about the film's background:

Q: What is “Badlapur” based on?

A: Basically it is an account written by a person (author Massimo Carlotto) who spent a lot of time in jail. He’s written quite a few stories, but many of his stories are actually about people he met in prison. The account he wrote is true but it happened elsewhere in the world. But some stories are universal, and I felt that this was a revenge story with a difference.

So although in interviews Raghaven frequently refers to his movie being based on real-life events, it appears he means based on the novel, which itself was supposedly based on real-life events. The implication in Raghavan's quote is that Carlotto met a prisoner whilst behind bars and Raghavan's movie is based on their story.

So now we move on to the key question - whilst Raghavan claims the novel is based on true events, is it really or is simply fiction?.

In an interview with The Guardian, Carlotto said:

'I have never once made up a killing,' he says. 'Every single death in everything I have written relates to a real killing, one for which I have read the autopsy report. I have seen the documents, I have carried out one-to-one interviews with murderers. This is my way of recording what is happening in present day Italy.

'The Noir writers talk about the social and political situation right now; they react very quickly to changes in the criminal world. In Italy, Mediterranean Noir is called the literature of reality. I even have journalists calling me when they are writing about crime, to ask me what is going on. The world of journalism has changed. There is no investigation now. Italy has lost any real sense of truth, because nobody believes the official "truths".

'It is very rare now for crime writers [in Italy] to invent stories. Most of them are real. Only the names are changed. That's why these books are so popular.'

And of course we now reach the problem. With the names changed, and without access to all the various autopsy reports and public records, it's impossible to verify whether the people in the book are actually real, are mostly real with fictional embellishments, or entirely fictional creations of Carlotto.

Carlotto hasn't given any interviews where has has proven the events - largely I suspect because he doesn't need to. And whilst the story is riveting, I doubt it's so unique that it would be easy to identify if it had really occurred.

The movie is based on real incidents that happened in 1990. The incident that happened is just known to have happened, there hasn't been an actual recording of the exact events. The film's story, however, follows those events closely, do just watch the film you'll get an idea of what happened. The book Death's Dark Abyss, just inspired the movie's theme and overall emotion, not the story.