Related Rule
Viet Nam
Practice Relating to Rule 101. The Principle of Legality
Viet Nam’s Criminal Code (2015), which includes war crimes, states:
Article 2. Basis of criminal liability
1. No one who commits a criminal offence that is not regulated by the Criminal Code has to incur criminal liability.
Article 7. Chronological effect of Criminal Code
1. A provision of law effective at the same time as the commitment of the criminal offence shall be applied to such criminal offence.
2. A provision of law that provides for a new crime, a more severe sentence, a new aggravating factor or reduce[s] the scope of suspended sentences, exemption from criminal liability, removal of criminal responsibility, exemption from sentence, commutation, or conviction expungement which is less favorable shall not be applied to criminal offences committed before such provision of law comes into force.
3. A provision of law that removes a new crime, a sentence, a[n] aggravating factor or provides for a less severe sentence, a new mitigating factor, or increase[s] the scope of probation, exemption or conviction expungement of criminal liability, exemption from sentence, commutation, conditional parole, or conviction expungement, and other provisions which [are] more favorable may be applied to criminal offences committed before such provisions of law come[] into force.
Article 29. Basis for exemption from criminal responsibility
1. A criminal offender shall be exempt from criminal responsibility on one of the following bases:
a) A policy or law is changed during the process of investigation, prosecution, or trial and accordingly, the offender’s act is no longer dangerous to society[.] 
Viet Nam, Criminal Code, 2015, Articles 2(1), 7 and 29(1)(a).