Genocidaires, from the French for ‘those who commit genocide

Genocide

Genocide is defined as "the deliberate and systematic destruction, in whole or in part, of an ethnic, racial, religious, or national group", though what constitutes enough of a "part" to qualify as genocide has been subject to much debate by legal scholars...

’, refers to those guilty of the mass killings of the 1994 Rwandan Genocide

Rwandan Genocide

The Rwandan Genocide was the 1994 mass murder of an estimated 800,000 people in the small East African nation of Rwanda. Over the course of approximately 100 days through mid-July, over 500,000 people were killed, according to a Human Rights Watch estimate...

, in which close to 1,000,000, primarily Tutsi

Tutsi

The Tutsi , or Abatutsi, are an ethnic group in Central Africa. Historically they were often referred to as the Watussi or Watusi. They are the second largest caste in Rwanda and Burundi, the other two being the Hutu and the Twa ....

 Rwandans, were murdered by their Hutu neighbors. In the aftermath of the genocide, those guilty of organizing and leading the genocide (the Genocidaires) were put on trial at the International Criminal Tribunal for Rwanda

International Criminal Tribunal for Rwanda

The International Criminal Tribunal for Rwanda is an international court established in November 1994 by the United Nations Security Council in Resolution 955 in order to judge people responsible for the Rwandan Genocide and other serious violations of international law in Rwanda, or by Rwandan...

. Those guilty of participating, profiting (eg through seizing Tutsi neighbors' property), etc. were put on trial in Gacaca courts.

It is also used as a term to broadly describe anyone who commits a genocide.