The Federal troops entered Asaba around 5 October, and began ransacking houses and killing civilians, claiming they were Biafran sympathisers. Reports suggest that several hundred may have been killed individually and in groups at various locations in the town. Leaders summoned the townspeople to assemble on the morning of 7 October, hoping to end the violence through a show of support for “One Nigeria.” Hundreds of men, women, and children, many wearing the ceremonial akwa ocha (white) attire paraded along the main street, singing, dancing, and chanting “One Nigeria.” At a junction, men and teenage boys were separated from women and young children, and gathered in an open square at Ogbe-Osowa village. Federal troops revealed machine guns, and orders were given, reportedly by Second-in-Command, Maj. Ibrahim Taiwo, to open fire. It is estimated that more than 700 men and boys were killed, some as young as 12 years old, in addition to many more killed in the preceding days.

The bodies of some victims were retrieved by family members and buried at home. But most were buried in mass graves, without appropriate ceremony. Many extended families lost dozens of men and boys. Federal troops occupied Asaba for many months, during which time most of the town was destroyed, many women and girls were raped or forcibly “married,” and large numbers of citizens fled, often not returning until the war ended in 1970. The total death toll during early October was in excess of 1,000, although the exact numbers will likely never be known.