Explain Expost facto law – double jeopardy.

The Indian Constitution, much like the U.S. Constitution, provides protections against ex post facto laws and double jeopardy, though with different nuances and contexts. Here's how they are treated under the Indian Constitution:

1. Ex Post Facto Law:

Article 20(1) of the Indian Constitution states that: "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."

   This means that the Indian Constitution protects individuals from being convicted under laws that were not in existence at the time the act was committed. The prohibition is specifically for criminal laws. Hence, any law that seeks to penalize or subject a person to a crime retrospectively is prohibited. However, civil obligations or liabilities can be imposed retrospectively.

2. Double Jeopardy:

   Article 20(2) of the Indian Constitution provides protection against double jeopardy: "No person shall be prosecuted and punished for the same offence more than once."

   This clause prevents an individual from being tried and punished more than once for the same offence. The essential elements to invoke this protection are:

• The person must be accused of an "offence".
• The person must have been "prosecuted" (which means legal proceedings must have been initiated).
• The person must have been "punished" for the same offence previously.

It's worth noting that being tried by a competent court and being convicted or acquitted is a necessary condition for this protection. If the first trial was vitiated or void due to any irregularities, the person can be tried again.

These provisions in the Indian Constitution are rooted in ensuring justice, individual liberty, and fairness. The principle against ex post facto criminal laws ensures predictability and reliability in the legal system, while the protection against double jeopardy safeguards individuals from being harassed and punished multiple times for the same offense.