Massacres are individual acts of mass killing of civilians or noncombatants, almost always characterised as having distinct political significance in shaping subsequent events.
Below is a list of incidents that are commonly referred to as massacres, though other incidents may also qualify yet not be called massacres.
... April 22 - Robert Oppenheimer, physicist (+ 1967)
May 6 - Harry Martinson, swedish author, winner of the Nobel Prize in literature
May 11 - Salvador Dalí, ...