In Dungo vs. People (G.R. No. 209464, July 1, 2015) the Supreme Court said that the better approach to distinguish between mala in se and mala prohibita crimes is the determination of the inherent immorality or vileness of the penalized act.
"If the punishable act or omission is immoral in itself, then it is a crime mala in se; on the contrary, if it is not immoral in itself, but there is a statute prohibiting its commission (for) reasons of public policy, then it is mala prohibita. In the final analysis, whether or not a crime involves moral turpitude is ultimately a question of fact and frequently depends on all the circumstances surrounding the violation of the statute."Therefore, the elements of mens rea must be proven in a prosecution for plunder. In the case of Estrada vs. Sandiganbayan (G.R. No. 148560. November 19, 2001), the Supreme Court agreed with Justice Mendoza in his concurring opinion which stated as follows:
"Precisely because the constitutive crimes are mala in se the element of mens rea must be proven in a prosecution for plunder. It is noteworthy that the amended information alleges that the crime of plunder was committed "willfully, unlawfully and criminally." It thus alleges guilty knowledge on the part of petitioner."