"I did not have to think much doing Bob Biswas in 'Kahaani'. Here in '89', he is far more dark and you can't read his mind," Saswata told PTI.
To get into the skin of serial killer Sabyasachi, Saswata prepared himself psychologically over a period of time.
"The very name of the thriller '89' suggests that there is suspense," the actor said hinting that there was a link between the title of the film and his character. He, however, did not reveal more.
Besides Saswata, Raima Sen and Barun Chanda are also acting in the film.
The film, selected for the 19th International Film Festival of Kerala (IFFK) 2014, had repeat screenings thrice and is due for travel to the US later.