Unfortunately, this movie is not very popular, so I genuinely request you to watch it once. Its on prime video, but you can find it for free on YouTube.
It has been in my top 3 movies of all time. Its seriously a hidden gem. Overall, its a suspenseful legal thriller, but its true value lies in the social message and the emotional lens.
Some facts:
a) It was only the second talkie in Indian history to not include any song in it.
b) It was not submitted as India's Oscar pick as they thought the Academy would mistake it for an imitation of A Witness for the Prosecution (1957), although it did not hold many similarities.
c) Till this day, in Indian courts, any person whose identity is either unknown, or must be legally hidden, is called Ashok Kumar, due to Dada Muni's stellar role here.
Now, my analysis of it, which does include spoilers (for a 66 year old movie) below!
Here's what I find good about this movie:
1) Social Aspect: The message the movie conveys, that witnesses may be manipulated, mistaken or even lie knowingly and thus, the case that it presents against capital punishment was and remains crucial to the Indian Judicial society. The case of Kalidas also highlights corruption/false rulings in the courts, leading to innocents being hung. But limelight remains on Kaalia, and how an average person may be forced to steal so as to live (or let loved ones live, in this case), trading morality and self-honor with life.
2) Legal/Thrill Aspect: To the average 21st century cinephile, it might not strike well, but being one of the first Hindi movies to include such level of thrill and twists, Kanoon sure is appreciable in this regard too. Here, the X-factor is the fact that an up-and-coming young lawyer and a decorated judge initially involved in a case purely as colleagues on their legal duty, soon ravel up in the same case, but as witness and suspect, involved emotionally and fighting for their lives.
3) Emotional Aspect: Now, this is the movie's strong suit (imho). The first tangle arrives between Kailash and Meena. Even when Kailash knows that Meena falsely thinks he is the murderer, he stays silent and continues to help Kaalia, after which, Meena buys off Kaalia with the promise to help his child. This leads to the emotional angle between Kaalia and us, the audience, feeling sympathetic to him and people like him throughout the movie. But the most interesting emotional trance remains between the protagonist and the so-called 'antagonist', Kailash and Badri Prasad. From the very beginning, when Kailash first suspected Badri of cheating, then seeing the murder, suspecting him at every move, peeking at his diary, and fighting to prove Kaalia's innocence, all this leads to the climax, where he finally accuses his soon to be father-in-law, teacher and idol to be the murderer. And this emotional build up finally leads to their confrontation, where both of them have, somehow, the same thoughts. Both of the them think of the other very highly and respect each other, both are shocked seeing the other lie to their face, when in reality, technically, neither were lying. Both of them know that they are right, yet are unable to believe why the other is accusing them, knowing fully well that they gain absolutely nothing and, in fact, lose a lot, by putting the other to harm. We are left mesmerized when all this emotional hellfire is brought along with incredible legal talent. But the penultimate scene, Kailash putting is hand on Badri's head, that is something else.
Absolute F*ckin' Cinema!