Saif Ali Khan stabbing case: How do law enforcement agencies use fingerprints to solve crimes?

How fingerprint analysis works

Law enforcement agencies use fingerprints in two situations.

Once an arrest is made for a crime, the prints of the accused are checked against a database of prints to establish if the arrested individual has a prior record of crime. Police can also lift prints from a crime scene and check them against the database. Under The Criminal Procedure (Identification) Act, 2022 (earlier, Identification of Prisoners Act, 1920) fingerprints of persons arrested for offences that carry a punishment of more than one year in jail can be stored.

Or, so-called “chance prints” lifted from the crime scene can be used as evidence to establish the presence of an accused on the scene. This is what is being attempted in the Saif Ali Khan case.

Lifting, matching prints

In Maharashtra, fingerprints are lifted either by experts of the state CID, or by officers who have been trained by these fingerprint experts. Prints are typically lifted off glass, metal, or plastic surfaces. Usually, only “proper” prints, in which the top third of a finger, which has the whorls and arches that form unique patterns in each individual, are considered.

The lifted prints are checked against the prints of the accused either digitally or by a fingerprint expert at the CID. Under the Henry Classification System of sorting fingerprints based on their physiological characteristics (developed by the English police officer Sir Edward Henry), a match of 10 points is considered a positive match, a former official of the fingerprint bureau in the CID said.

Smudged samples return an inconclusive result.

One print is enough

Multiple individuals, including the victim, could leave prints at the scene of a crime; also, it is not necessary that an accused leave proper prints of all their fingers. Police require a match of just one finger on either hand of an accused to establish their presence at the crime scene.

Prints of all 10 fingers of arrested accused are sent to the CID to check if any one of them matches with those lifted from the scene.

Mumbai Police’s version

Mumbai Police have said that they are still waiting for the final report of the CID on the prints they have lifted from the crime scene. They have not confirmed how many prints they have sent to the CID.

An official said that under the Bharatiya Nagrik Suraksha Sanhita, investigators are required to make a video recording of the entire panchnama process along with timestamps so as to maintain transparency.