There is an old English legal doctrine, more than 300 years old, that says that if two people participate in a crime, then they are all criminally liable for the results of each other's actions regardless of who actually committed the crime.
Over time, however, this legal doctrine has been expanded to what is now known as Joint Criminal Enterprise (JCE). Simply put, the new legal doctrine says that if a person is a member of a criminal enterprise, he is responsible for the reasonable and foreseeable consequences of the actions of that enterprise.
It is a development of the law that has become so controversial that some legal scholars term it outright unconstitutional - it makes one liable not for anything they did, but because they are associated with people who did it. The doctrine has therefore come to be cynically referred to as "Guilt by Association".
The doctrine properly found its way from national to international law in the Nuremberg trials after WWII. One of the problems facing the prosecutors at the military tribunal was that it was difficult to get evidence that showed each accused committing murder. Yet each of them was a high ranking Nazi soldier. The view of the prosecutors became that since the stated policy of the Nazi regime was the extermination of Jews, then any person serving the regime knowing fully well its criminal intentions was liable for its actions.
Using this approach, the military tribunal convicted numerous Nazi soldiers based not on their actions but their membership and position of authority in the regime.
After the Nuremberg trials, there were no major international crimes for about 50 years. During this period, the JCE doctrine was re-adopted by national laws and used to pursue criminal organisations. In the US, it was found particularly invaluable in pursuing memners of the Mafia and putting them behind bars.
With the establishment of the International Criminal Tribunal for the former Yugoslavia in 1993, the JCE doctrine re-entered international criminal law in a most frightening fashion. So revolutionary was its application by the Tribunal that respected lawyer and author John Laughland, in his book Travesty: The Trial of Slobodan Milosevic and the Corruption of International Justice, states, "The International Criminal Tribunal for the former Yugoslavia... has invented a doctrine of criminal liability known as 'joint criminal enterprise'. It uses this concept, which is so contentious that it is unconstitutional in many jurisdictions, in order to convict people of crimes when even the Tribunal accepts that they did not, in fact, commit them or that the proof is lacking to show that they did." He staes in jest that JCE stands for "Just Convict Everyone".
The bone of contention was a limb of criminal liability that the Tribunal added to the JCE called the "extended" or "category three" Joint Criminal Enterprise. It states that a person will be criminally liable for crimes committed during the carrying out of a common plan if those plans, though not part of the common plan and not intended by him, are a natural and foreseeable consequence of carrying out the commom purpose. The Tribunal gave an example that if people join in a common plan to evict members of one ethnic group from their homes at gunpoint, and in the process those doing the evictions carry out killings, then everyone involved in the planning of the evictions or contributed to the plan in any way is guilty for the killings, even if they did not intend that outcome.
The JCE doctrine has been adopted by international criminal tribunals on Sierra Leone and Rwanda, and accepted as "now settled law under customary international law". This extended JCE is the foundation of the cases that ICC prosecutor Luis Moreno-Ocampo will be pursuing against the Ocampo 6.