Massacres of Poles had been taking place since the invasion of Poland.  

Poles were the first victims of the Germans in Poland from the start of the invasion on September 1, 1939.

One of the best-documented cases of these massacres took place on 20–21 June 1940, when 358 members of the Polish political, cultural, and social elite were murdered in a single operation. Palmiry is one of the most infamous sites of German crimes in Poland and "one of the most notorious places of mass executions" in Poland.

Between December 1939 and July 1941, more than 1700 Poles and Jews – primarily inmates of Warsaw's Pawiak prison – were executed by the S.S. (Schutzstaffel) and Ordnungspolizei in a forest clearing near Palmiry. 

Along with the Katyn massacre, it has become emblematic of the martyrdom of Polish intelligentsia during World War II.

On October 8, 1939, about 354 Polish teachers and catholic priests were detained because occupational authorities assumed that they were "full of Polish chauvinism" and "created an enormous danger" for public order. Soon Warsaw's prisons and detention centers like the Pawiak, Mokotów Prison, the Central Detention Center at Daniłowiczowska Street, and the cellars of the Gestapo headquarter on 25 Szucha Avenue were full of inmates. Many of the prisoners were deported to Nazi German concentration camps. Many others were murdered.

Warsaw was one of the biggest obstacles for the Germans as for Polish resistance as well as for a center of Polish intelligentsia. 

On December 14, 1943, Governor-General Hans Frank noted in his diary:

"There is a one place in this country which is a source of all our misfortunes – it is Warsaw. Without Warsaw we wouldn't have four-fifths of the troubles which we're facing now. Warsaw is the focus of all disturbances, the place from which discontent is spread through the whole country"

In the first months of German occupation, political prisoners from Warsaw were secretly executed in the back of the Polish parliament (Sejm) building complex at Wiejska Street (in the so-called Sejm gardens, ogrody sejmowe). Between October 1939 and April 1940, several hundred people were murdered in this place. 

However, German police authorities soon realized that they would not be able to keep executions secret if they were conducted in the very center of a large city. It was decided that henceforth mass executions would be carried out in the small forest glade in Kampinos Forest, located near the villages of Palmiry and Pociecha, about 30 kilometers (19 mi) northwest of Warsaw.

Executions in Palmiry were carried out by the members of the Ordnungspolizei or by the SS-Reiterei  (S.S. Cavalry) regiment, which was quartered in Warsaw. They were overseen by Gestapo officers led by the S.D. and Sicherheitspolizei Commander in Warsaw, SS-Standartenführer Josef Meisinger.

In every case, mass executions in Palmiry were prepared carefully so as not to cause suspicion. Mass graves were always dug a few days before the planned execution. Usually, it was done by the Arbeitsdienst unit, quartered in Łomna, or by Hitlerjugend members who camped near Palmiry. In most cases, the graves were shaped like a ditch and were more than 30 meters (98 ft) long and 2.5–3 meters (8 ft 2 in–9 ft 10 in) deep. 

Sometimes, irregularly shaped graves were prepared for smaller groups of convicts or for individual victims, similar to natural terrain landslides or explosion craters. The clearing where executions took place was soon enlarged by tree-cutting. Polish forestry workers always received a day off on the day of the planned execution. In the meantime, German police undertook intensive patrolling near the clearing and surrounding forest.

Victims were transported to the place of execution by trucks. Usually, they were brought from Pawiak prison, rarely from Mokotów Prison. S.S. soldiers tried to convince their victims that they would transfer them to another prison or a concentration camp. For this reason, death transports were usually formed at dusk, and prisoners were allowed to take their belongings with them. 

Sometimes before departure, convicts received an additional food ration and were given back their documents from the prison's depository. Initially, these methods were so effective that the prisoners were not aware of the fate awaiting them.

Later, when the truth about what was happening in Palmiry, news spread through Warsaw, some victims tried to throw short letters or small belongings from the trucks, hoping that they would be able to inform their families about their fate. During postwar exhumation, some bodies were found with a card reading "Executed in Palmiry", written by the victims shortly before their death.

How despicable of the Germans to do such a thing to the Polish, that had no opportunity to fight back. This was cold-blooded murder. 

The prisoners' bags were taken at the glade, but they were permitted to keep their documents and small belongings. Jews could keep their yellow badges, and people who worked in Pawiak's infirmary could keep their badges with the Red Cross symbol. Sometimes prisoners' hands were tied and their eyes blindfolded. The victims were then taken to the edge of the grave and executed by machine gunfire. Sometimes victims were forced to hold a long pole or ladder behind their back. Such supports were later lowered so that the bodies fell into the grave in an even layer. Postwar exhumation proved that the wounded victims were sometimes buried alive. 

S.S. and OrPo members photographed the executions until it was forbidden by the SS-Standartenführer Meisinger, as happened on May 3, 1940. After the execution was finished, the graves were filled in, covered with moss and needles, and then planted over with young pine trees. Families of the victims were later informed by the Nazi authorities that their relatives had "died from natural causes." 

Despite all efforts, the Nazi Germans were not able to keep the massacres secret. Local Polish inhabitants, especially forestry workers and inhabitants of Palmiry and Pociecha, had many opportunities to observe the death transports and to hear the gunshots. Several times they also saw groups of convicts being led to the place of execution. Forester Adam Herbański and his subordinates from the Polish Forest Service helped reveal the truth about the Palmiry massacre. 

At the risk of their lives, they visited the forest glade after the executions (usually at night) in order to secretly mark out the mass graves. Also, a few photos taken by the executioners in Palmiry were stolen by Union of Armed Struggle members.

According to Polish historians, between 700 and 900 people were executed in Palmiry from December 1939 until April 1940. Many of these people just happened to be at the wrong place at the wrong time at were rounded up for retaliation. Others were targeted. 

In the spring of 1940, the highest NSDAP and S.S. authorities in the General Government decided to conduct a wide-ranging police operation to exterminate the Polish political, cultural, and social elite. The mass murder of Polish politicians, intellectuals, artists, social activists, and people suspected of potential anti-German activity was seen as a preemptive measure to keep the Polish resistance scattered and prevent the Poles from revolting during the planned German invasion of France. This operation was given the code name AB-Aktion (shortcut from Außerordentliche Befriedungsaktion). It lasted from May to July 1940 and claimed at least 6,500 lives.

At the end of March 1940, Warsaw and surrounding cities were hit by a wave of arrests. During the next two months, hundreds of Polish intellectuals and prewar politicians were detained and imprisoned in Pawiak. On April 20, the Gestapo arrested 42 Polish attorneys in Warsaw's Chamber of Attorneys building. On May 10, occupants detained over a dozen Polish school principals who, despite the German interdict, had closed their school on May 3 Constitution Day. The frequency and number of executions in Palmiry increased with the beginning of AB-Aktion. 

The first mass execution conducted in Palmiry in the course of AB-Aktion took place on June 14, 1940. About 20 people were murdered that day, among them Polish historian Karol Drewnowski and his son Andrzej. 

The best-documented massacre took place on 20–21 June 1940 when three transports with 358 inmates were sent from Pawiak to the place of execution near Palmiry. Among the victims were:

• Maciej Rataj (politician, former Marshal of the Sejm)

• Mieczysław Niedziałkowski (politician of the Polish Socialist Party)

• Jan Pohoski  (prewar deputy president of Warsaw)

• Ludomir Skórewicz  (prewar starosta of Warsaw powiat)

• Halina Jaroszewiczowa (politician, former member of parliament)

• Henryk Brun (industrialist, former member of parliament, chairman of the Polish Merchants Association)

• Janusz Kusociński (athlete, winner of the 10,000 m race at the 1932 Summer Olympics)

• Feliks Zuber (athlete, deputy president of "Warszawianka" sport club)

• Tomasz Stankiewicz (track cyclist who competed in the 1924 Summer Olympics)

• Jan Wajzer (doctor of law, secretary general of the Polish Union in Free City of Danzig)

• Stefan Kwiatkowski (deputy chairman of the Association of teachers of secondary and third degree schools)

• Władysław Dziewałtowski-Gintowt, Tadeusz Fabiani Edmund Grabowski, Czesław Jankowski [pl], Stanisław Jezierski, Józef Krasuski, Jerzy Niżałowski, Józef Starzewski, Wacław Tyrchowski (attorneys)

• Stanisław Beer, Jadwiga Fuks, Maria Witkowska (painters);

• Helena Łopuszańska  (actress)

• Agnieszka Dowbor-Muśnicka (activist and daughter of General Józef Dowbor-Muśnicki)

• Alicja Bełcikowska, Jan Bełcikowski, Grzegorz Krzeczkowski, Wojciech Kwasieborski, Tadeusz Lipkowski, Jan Werner (writers and publicists)

Last executions

SS-Gruppenführer Paul Moder's announcement of execution of "a number of Poles" in retaliation of death of Igo Sym.

On July 23 1940, Governor-General Hans Frank officially announced the end of AB-Aktion. Despite that, massacres in Palmiry continued for over a year. On August 30 1940, at least 87 persons were executed at the forest glade. Among the victims were several people who were arrested in Włochy three months earlier. 

Another mass execution was carried out on September 17, 1940, when about 200 prisoners of Pawiak, including 20 women, were murdered at the forest clearing near Palmiry. Among the victims were: Tadeusz Panek and Zbigniew Wróblewski (attorneys), Fr. Zygmunt Sajna (parson of Catholic parish in Góra Kalwaria), Jadwiga Bogdziewicz and Jan Borski (journalists) and Władysław Szopinski. According to Regina Domańska, this massacre might be connected to uncovering an underground printing house at Lwowska Street in Warsaw. 

This was the last execution conducted in Palmiry in 1940, for which circumstances are at least partially known. However, during the postwar exhumation, three mass graves filled with 74, 28, and 24 corpses respectively, were found at the forest glade. It is certain that first two of them were filled and buried in the winter of 1940, while the third one was probably dug in the winter of 1940 or 1939.

Polish historians were not able to determine the circumstances of those massacres. According to Regina Domańska, about 27 prisoners of Pawiak were executed in Palmiry on December 4, 1940. According to Maria Wardzyńska, up to 260 people could have been murdered in Palmiry in the winter of 1940. 

On March 7, 1941, actor Igo Sym, a well-known German Nazi collaborator and Gestapo agent, was assassinated by the soldiers of the Union of Armed Struggle. In retaliation, 21 Pawiak prisoners were executed in Palmiry four days later. Among the victims were Stefan Kopeć (biologist, professor at the University of Warsaw) and Kazimierz Zakrzewski (historian, professor at the University of Warsaw). 

On April 1, 1941, about 20 men from Łowicz were executed in Palmiry. Among the victims was the deputy mayor of Łowicz, Adolf Kutkowski. 

Another massacre was conducted on June 12, 1941, when 30 prisoners of Pawiak, including 14 women, were murdered in Palmiry. Among the victims were: Witold Hulewicz (poet and radio journalist), Stanisław Piasecki (right-wing politician and literary critic), Jerzy Szurig (lawyer, syndicalist), Stanisław Malinowski (attorney). 

The last known mass execution in Palmiry was carried out on July 17 1941 when 47 people, mostly prisoners of Pawiak, were murdered in the forest glade. Among the victims were Zygmunt Dymek (journalist and labor activist) and six women. 

After July 17, 1941, German authorities ceased using the forest glade in Palmiry as a place of mass executions. The reason probably was that they realized the Polish resistance and the civilian population were well aware of what was happening in Palmiry.

After the war, the Polish Red Cross, supported by the Chief Commission for the Investigation of German Crimes in Poland, began the search and exhumation process in Palmiry. The work was carried out between November 25 and December 6 1945, and later from March 28 until the first months of summer 1946. Thanks to Adam Herbański and his subordinates from the Polish Forest Service, who in the years of occupation were risking their own lives to mark the places of execution, Polish investigators were able to find 24 mass graves. 

More than 1700 corpses were exhumed, but only 576 of them were identified. Later Polish historians were able to identify the names of another 480 victims. It is possible that some graves still lie undiscovered in the forest near Palmiry. 

In 1948 the forest glade near Palmiry was transformed into a war cemetery and a mausoleum. Victims of German terror whose bodies were found in some other places of execution within the so-called "Warsaw Death Ring" were also buried in the Palmiry cemetery. Altogether, approximately 2204 people are buried there. In 1973, the Palmiry National Memorial Museum, a branch of the Museum of Warsaw, was created in Palmiry. 

Fr. Zygmunt Sajna, who was murdered in Palmiry on September 17, 1940, is one of the 108 Polish Martyrs of World War II beatified on June 13, 1999, by Pope John Paul II. Fr. Kazimierz Pieniążek (member of the Resurrectionist Congregation), another victim of the Palmiry massacre, has been accorded the title of Servant of God. He is currently one of the 122 Polish martyrs of the Second World War included in the beatification process initiated in 1994. 

Palmiry has become, as Richard C. Lukas puts it, "one of the most notorious places of mass executions" in Poland. It is also one of the most famous sites of Nazi crimes in Poland. Along with the Katyn Forest, it became a symbol of the martyrdom of the Polish intelligentsia during the Second World War. In 2011 Polish president Bronisław Komorowski said, "Palmiry is to some extent the Warsaw Katyn."