Articles 20, 21 and 22 provide a system of protection, relevant to the criminal law. Article 20 guarantees to all persons — whether citizens or non-citizens-three rights namely:—

• Protection against ex-post facto laws

According to Article 20(1), no person shall be convicted of any offence except for violation of a law in force at the time of the commission of the act charged as an offence, nor be subjected to a penalty greater than that which might have been inflicted under the law in force at the time of the commission of the offence.

Ex-post facto laws are laws which punished what had been lawful when done. If a particular act was not an offence according to the law of the land at the time when the person did that act, then he cannot be convicted under a law which with retrospective declares that act as an offence. For example, what was not an offence in 1972 cannot be declared as an offence under a law made in 1974 giving operation to such law from a back date, say from 1972.

Even the penalty for the commission of an offence cannot be increased with retrospective effect. For example, suppose for committing dacoity the penalty in 1970 was 10 years imprisonment and a person commits dacoity in that year. By a law passed after his committing the dacoity the penalty, for his act cannot be increased from 10 to 11 years or to life imprisonment.

In Shiv Bahadur Singh v. State of Vindhya Pradesh, AIR 1953 S.C. 394, it was clarified that Article 20(1) prohibited the conviction under an ex post facto law, and that too the substantive law. This protection is not available with respect to procedural law. Thus, no one has a vested right in procedure. A law which nullifies the rigour of criminal law is not affected by the rule against ex post facto law (Rattan Lal v. State of Punjab, (1964) 7 S.C.R. 676).

• Protection against double jeopardy

According to Article 20(2), no person shall be prosecuted and punished for the same offence more than once. It is, however, to be noted that the conjunction “and” is used between the words prosecuted and punished, and therefore, if a person has been let off after prosecution without being punished, he can be prosecuted again.

• Protection against self-incrimination

According to Article 20(3), no person accused of any offence shall be compelled to be a witness against himself. In other words, an accused cannot be compelled to state anything which goes against him. But it is to be noted that a person is entitled to this protection, only when all the three conditions are fulfilled:

1. that he must be accused of an offence;
2. that there must be a compulsion to be a witness; and
3. such compulsion should result in his giving evidence against

So, if the person was not an accused when he made a statement or the statement was not made as a witness or it was made by him without compulsion and does not result as a statement against himself, then the protection available under this provision does not extend to such person or to such statement.