Passage: Most of the population, urban and rural, took out their anger and frustrations on the nation's Vietnamese population. Lon Nol's call for 10,000 volunteers to boost the manpower of Cambodia's poorly equipped, 30,000-man army, managed to swamp the military with over 70,000 recruits. Rumours abounded concerning a possible PAVN offensive aimed at Phnom Penh itself. Paranoia flourished and this set off a violent reaction against the nation's 400,000 ethnic Vietnamese.Lon Nol hoped to use the Vietnamese as hostages against PAVN/Viet Cong activities, and the military set about rounding them up into detention camps. That was when the killing began. In towns and villages all over Cambodia, soldiers and civilians sought out their Vietnamese neighbors in order to murder them. On 15 April, the bodies of 800 Vietnamese floated down the Mekong River and into South Vietnam.

Question: How many Vietnamese were killed during the April 15 mass murder?
800