The genocide was organised by members of the core Hutu political elite, many of whom occupied positions at top levels of the national government. Most historians agree that a genocide against the Tutsi had been planned for at least a year. However the assassination of Rwandan president Juvénal Habyarimana on 6 April 1994 created a power vacuum and ended peace accords. Genocidal killings began the following day when soldiers, police, and militia executed key Tutsi and moderate Hutu military and political leaders.
Following Habyarimana's death, on the evening of 6 April, a crisis committee was formed; it consisted of Major General Augustin Ndindiliyimana, Colonel Théoneste Bagosora, and a number of other senior army staff officers. The committee was headed by Bagosora, despite the presence of the more senior Ndindiliyimana. Prime Minister Agathe Uwilingiyimana was legally next in the line of political succession, but the committee refused to recognise her authority. Roméo Dallaire met with the committee that night and insisted that Uwilingiyimana be placed in charge, but Bagosora refused, saying Uwilingiyimana did not "enjoy the confidence of the Rwandan people" and was "incapable of governing the nation". The committee also justified its existence as being essential to avoid uncertainty following the president's death. Bagosora sought to convince UNAMIR and the RPF that the committee was acting to contain the Presidential Guard, which he described as "out of control", and that it would abide by the Arusha agreement.
On 7 April, as the genocide started, RPF (the Rwandan Patriotic Front) commander Paul Kagame warned the crisis committee and UNAMIR that he would resume the civil war if the killing did not stop.
On 10–11 April 1994, UNPROFOR called in air strikes to protect the Goražde safe area, resulting in the bombing of a Serbian military command outpost near Goražde by two US F-16 jets.
Thousands sought refuge in the Official Technical School (École Technique Officielle) in Kigali where Belgian UNAMIR soldiers were stationed. On 11 April, the Belgian soldiers withdrew, and Rwandan armed forces and militia killed all the Tutsi.
On 12 April, the Belgian government, which was one of the largest troop contributors to UNAMIR, and had lost ten soldiers protecting Prime Minister Uwilingiliyimana, announced that it was withdrawing, reducing the force's effectiveness even further.
Nixon suffered a severe stroke on April 18, 1994, while preparing to eat dinner in his Park Ridge, New Jersey home. A blood clot resulting from the atrial fibrillation he had suffered for many years had formed in his upper heart, broken off, and traveled to his brain. He was taken to New York Hospital–Cornell Medical Center in Manhattan, initially alert but unable to speak or to move his right arm or leg. Damage to the brain caused swelling (cerebral edema), and Nixon slipped into a deep coma.
Around 29 April 1994, a Danish contingent (Nordbat 2) on peacekeeping duty in Bosnia, as part of UNPROFOR's Nordic battalion located in Tuzla, was ambushed when trying to relieve a Swedish observation post (Tango 2) that was under heavy artillery fire by the Bosnian Serb Šekovići brigade at the village of Kalesija.