To know the truth CBI) is a 2005 Indian Malayalam-language mystery film directed and produced by K. Madhu and written by S. N. Swamy.

The fourth installment in the franchise of CBI investigative thrillers, Mammootty reprised the role of Sethurama Iyer, a Central Bureau of Investigation officer, with Mukesh and Jagathy Sreekumar reprising their roles as the associate officers Chacko and Vikram, respectively, and the background score composed by Shyam.

Apart from Mammootty, Mukesh, and Jagathi Sreekumar who comprised the team of CBI investigators, Nedumudi Venu, Thilakan, Samvrutha Sunil, Gopika, Suja Karthika, and Jishnu were added to the cast to play other prominent roles in the film.

[1] A critic from Sify assessed the film as "good'" and lauded S.N.Swamy for "making something spectacular out of ordinary material", the "mood enhancing" background score by Shyam, and the "commendable" cinematography of Salu George, noting that "The highlight of the film is Mammootty as the suave and intelligent Sethurama Iyer who looks dashing and debonair.

Another interesting highlight is the war of words between Iyer and Kapra (Thilakan), a local sorcerer which ignites the screen."