Short answers, pulled from the story.
The Palmiry massacre was a series of mass executions carried out by Nazi German forces during World War II in a forest glade near the village of Palmiry, in the Kampinos Forest northwest of Warsaw. Between December 1939 and July 1941, the SS and Ordnungspolizei murdered more than 1700 Poles and Jews there, most of them prisoners from Warsaw's Pawiak prison.
The killings at Palmiry took place between December 1939 and July 1941. The best documented massacre happened on the 20th and the 21st of June 1940, when 358 members of Poland's political, cultural and social elite were executed in a single operation.
Victims of the Palmiry massacre included Polish and Jewish prisoners from Warsaw's Pawiak prison, along with members of Poland's political, cultural and social elite. Notable victims included Maciej Rataj, a former Marshal of the Sejm and acting President of Poland, and the Olympic athlete Janusz Kusociński, winner of the 10,000 meter race at the 1932 Summer Olympics.
German police authorities moved executions to the forest glade near Palmiry after realizing they could not keep killings secret while carrying them out in the center of Warsaw at the Sejm gardens. The glade in the Kampinos Forest, about 30 kilometers northwest of Warsaw, allowed for greater secrecy.
After the war, the Polish Red Cross and the Chief Commission for the Investigation of German Crimes in Poland exhumed the site, guided by markers that forester Adam Herbański and his Polish Forest Service colleagues had secretly placed during the occupation. Investigators located 24 mass graves and identified 576 of the exhumed dead at the time, later adding 480 more names.
Some of those responsible were tried after the war. Ludwig Fischer, governor of the Warsaw district, and Josef Meisinger, the SD and Sicherheitspolizei commander in Warsaw, were sentenced to death by the Supreme National Tribunal in Warsaw on the 3rd of March 1947 and hanged at Mokotów Prison that same month.