Vijay, an accused, committed an offence of dacoity in 2015. At that time dacoity was punishable with imprisonment of 10 years. In 2016 during his trial, a law was passed which made dacoity punishable with life imprisonme

According to Article 20(1) of the Constitution of India, 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 retrospectively declares that act as an offence. Even the penalty for the commission of an offence cannot be increased with retrospective effect. In the given case, for committing dacoity the punishment in 2015 was 10 years imprisonment and Vijay commits dacoity in that year. By a law passed after his committing the dacoity the punishment, for his act cannot be increased to life imprisonment, because punishment cannot be increased retrospectively.