The 47-year-old will be seen as Inspector Surjan Singh Shekhawat in the film for which many scenes were shot after sunset.
"Almost all of the major scenes have been shot during the night. Since the shooting would take place after sunset, there would be cops on the sets. Aamir often chatted with them asking details about their work and inquiring about the places that they would visit often," a source said.
Directed by Reema Kagti, "Talaash", is a thriller that also stars Kareena Kapoor and Rani Mukerji. Slated for a Nov 30 release, the film has been co-written by Kagti and Zoya Akhtar.
"Night seems to be a key player in the film's storyline. The idea of making this film had also stemmed from an incident involving cops that was witnessed by Zoya and Reema who then wrote this project," another source added.