It is convenient to start with customary law as this is both the oldest source and generates rules binding on all States. Law alters customary international law. Customary international law results from states' general and consistent practice that they follow from a sense of legal obligation. Two examples of customary international laws are the doctrine of non-refoulment and the granting of immunity for visiting heads of state.

Acceptable norms and values generally recognized form the basis of customs as a sources of international law. It has its root from the Jurisprudence of Natural Law., The violation of which is offensive to the conscience of humanity.

Customary law is considered primary authority, some reaching the

level of peremptory law or jus cogens when established as a fundamental principle and become non-derogable. Jus cogens and even other customs can become general principles through codification or when recognized by international courts.

Criminal laws, are laws that have diverse interpretations.costoms and traditional laws most of the time goes against the justice system.eg.in sierra Leone, Liberia and Guinea.young children normally, before adult hood are forced into genital mutilation.But Activist and gender human rights have ratified such practices to be classified as criminality.

The customs and general principles form the basis of international criminal law if it fulfils the requirements of “a general practice accepted as law“, as laid down in Article 38 of the Statute of the International Court of Justice, also Article 3 of the Statute of the Hague International Criminal Tribunal, which grants equal standing to the laws and customs of war as a basis for trial and conviction

International customs and legal precedents have served as the foundation for development of the criminal law in newly established countries/nations and in newly formed constitutionally formed systems of government. Perhaps the best example of this the development of the criminal law in the United States, Canada, New Zealand and other United Kingdom countries based on Anglo Saxon legal principles.

As a financial crime practitioner of some 30 years experience, I've seen this evolve and would take a slightly different tack/perspective. Broadly speaking the evolution of international law on FC has been driven by 3 factors. a) The FATF principles which have (arguably) directly influenced/shaped FC law across the globe from its outset. This was based on common FC practice principles (rather than any specific aspect of the law - Common or civil). b) The UK FC legal framework (partic the various iterations of: the Money Laundering Regs, the Proceeds of Crime Act, the Bribery Act and the Fraud Act) have been disproportionately influential due to: i) the proliferation of equivalent legislation across common law jurisdictions, ii) the importance of UK as a fin services centre. c) US FC related law - eg Patriot Act, due to i) The global importance of US fin services/dollar denominated transactions; ii) the extra territoriality claimed by the US for its legislation - and its willingness to follow through on alleged infractions by foreign firms operating in US/doing $ denominated business. So, in so far as their actually is any such thing as international law on FC (eg UN sanctions are non binding/legally enforceable) the key drivers tend to be the frameworks established in US/UK, together with FATF practitioner based good practice recommendations (predominently set by UK and US based senior practitioners",. Just my view though

Costumary laws seeks to fit with the traditions and cultural norms practice and values of a community setting