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Prosecuting War Crimes in Ukraine


What students of international human rights need to know

By Ellen J. Kennedy, Ph.D.

The worst crimes in the world are known as the four core international crimes: genocide, war crimes, crimes against humanity, and aggression. Although these terms are used widely in the news, especially in reference to crimes occurring in today’s war in Ukraine, distinctions between them are not widely known.

This paper defines the unique elements of each of these crimes; the international, regional, and national mechanisms by which perpetrators can be prosecuted; and current efforts to end impunity for the core international crimes that are occurring in Ukraine.

The crimes

Raphael Lemkin was a Polish Jew who fled from the Nazi invasion of Poland in 1939, eventually arriving in the United States. He tried unsuccessfully to get his family out of Europe, but 49 members of his extended family perished, including his parents, at Auschwitz, in the Warsaw ghetto, and on death marches.1 

At that time there were words to describe the killing of a person—homicide, suicide, fratricide, etc.—but there was no word to describe the killing of an entire people, the situation that was unfolding with the extermination of Europe’s Jews.

Lemkin was a jurist, having received his legal training in Lviv, Ukraine, and a linguist. He took the Greek root ‘genos,’ meaning tribe or group or people, and the Latin verb ‘cidere,’ meaning to kill, and coined the word genocide to refer to the killing of a people. Once he had the word, he sought legal means to prevent and punish the crime. He wrote the Convention on the Prevention and Punishment of the Crime of Genocide and he dedicated himself to advancing its ratification at the United Nations, which occurred in 1948.

The United States didn’t ratify the Genocide Convention until 1988, and then only due to the persistence of Sen. William Proxmire of Wisconsin, who gave 3,211 speeches on the floor of the Senate—a speech a day for 19 years, each one unique—until the Senate finally cast the required 67 YES votes for ratification, passing it with a vote of 93-1.2 The hesitation was that the US could be found culpable of this crime of genocide for atrocities perpetrated against the indigenous people and against Blacks.

The U.S. ratification, however, under the dualist process by which international treaties become U.S. domestic law,3 was accompanied by so many RUDs, (reservations, understandings, and declarations) as to render the Convention largely toothless in requiring any U.S action in response to genocide. And in an ignominious end to the ratification saga in the U.S., President Ronald Reagan signed the Convention into law in an airplane hangar at Chicago’s O’Hare Airport, 40 years after it was ratified by the UN.4

The Genocide Convention defines the crime as “the intent to destroy, in whole or in part, a national, ethnic(al), racial, or religious group.” Genocide involves killing members of the group; causing serious bodily or mental harm; deliberately inflicting conditions to bring about the group's physical destruction in whole or in part; preventing births within the group; and forcibly transferring children of the group to another group.5

The UN reported that as of March 26, 2023, at least 8,400 civilians have been murdered in Ukraine, 429 of them children.6 Putin’s forces have attacked more than a thousand towns, leaving residents without food, water, heat, light, or medicine; prevented births by bombing maternity hospitals; displaced 7 million people inside the country with explosives and artillery; forced 8.2 million people,7 mostly women and children, to flee across Ukraine's borders for safety; and transferred at least 13,000 children to Russia for forced adoptions.8 It appears that, as a recent article in Foreign Affairs concluded, “with every passing day, it is becoming clearer that Russia is committing the gravest crime imaginable in Ukraine: genocide,”9 with similar words issued by the United States Institute of Peace: “Officials and experts are becoming increasingly convinced that Russia is committing genocide against the Ukrainian people.”10

Crimes against humanity are similar to genocide in their brutality, but they are widespread attacks against any civilian population, not against a specific national, ethnic, racial, or religious group. This core international crime includes murder, extermination, enslavement, deportation, and other inhuman acts committed against any civilian population. Crimes against humanity were defined at the post-World War II Nuremberg trials as the means to hold individuals accountable for the worst of the Third Reich’s atrocities.11

Unlike the crime of genocide, crimes against humanity have not been codified with an international convention. That process is currently underway through the Crimes Against Humanity Initiative, which first published a proposed convention in 2010. The UN General Assembly’s Sixth Committee, which reviews legal issues, will consider the current version in meetings from April 10-14, 2023.12

International laws have created the foundation for codifying crimes against humanity. The International Criminal Court is the world’s first permanent court established to prosecute individuals for the four core international crimes of genocidecrimes against humanitywar crimes, and aggression. The Rome Statute, the foundational document of the court, gives definitions for these crimes that are used in proceedings throughout the world. Crimes against humanity, as enumerated in the Rome Statute, include 15 egregious offenses such as murder, rape, imprisonment, enforced disappearances, enslavement—particularly of women and children—sexual slavery, torture, apartheid, and deportation.13 These atrocities can occur during genocides as well, but the key distinction is that crimes against humanity consist of atrocities carried out against a widespread and general population.

When the war began in Ukraine, 285,000 foreigners were permanent residents in the country and there were thousands of temporary residents as well, including 16,000 African students.14 They, too, are victims in this war, although they are not Ukrainian. Acts of violence against them fall under the definition of crimes against humanity, not genocide.

Aggression is the illegal use of force, invasion, bombardment, and military occupation by one state upon another state. In a statement from the Nuremberg proceedings, aggression is defined as follows: “The crime of aggression is the supreme international crime, differing only from other war crimes in that it contains within itself the accumulated evil of the whole.”15 Aggression is “the invasion of a state by the armed forces of another state,” according to the United Nations.16

Up until the early 20th century, waging war was not prohibited under international law, and states could use war as a legitimate political instrument. But the Covenant of the League of Nations in 1920 brought about a shift. The 63 member states of the League of Nations obliged themselves “to respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League.”17 Interestingly, although U.S. President Woodrow Wilson was a strong proponent of the League, the U.S. never joined; isolationists in the Senate voted against ratification.18

In the subsequent Kellogg-Briand Pact of 1928, which the US ratified, war as an instrument of national policy was abandoned. The Kellogg-Briand Pact became the foundation for the trial of Nazi leaders in 1946.

After World War II, the UN Charter of 1945 prohibited the threat or use of force against the territory or political independence of any state, in what became defined as the crime of aggression. However, two exceptions were made: first, for self-defense, and second, if the UN Security Council authorized the use of force.19

Russia’s illegal aggression that began on February 24, 2022 is the worst violence in Europe since World War II.20

War crimes constitute the fourth core international crime. Essential elements of war crimes include murdering prisoners of war and civilians; committing crimes against aid workers and peacekeepers; destroying cities, towns, and monuments; and using poisonous and prohibited weapons.

The UN, the European Union, and 45 nations have accused Russia of war crimes in Ukraine, and they charge Putin with responsibility for those crimes.21

War crimes, like genocide, are codified in international law. The first formal codification began with the Lieber Code (1863) in the U.S. Civil War, followed by the Hague Conventions of 1899 and then 1907 for international war. In 1949, the Geneva Conventions defined new war crimes.

The Hague and Geneva Conventions were among the first formal statements of the laws of war and war crimes in international law. This combined body of law, the law of war, is known as international humanitarian law (IHL) because of prohibitions on attacking humanitarian aid organizations, prisoners, and civilians. These related treaties were adopted and expanded from 1864 to 1949 and represent a legal basis for conducting war under international law.22 Every member state of the UN has ratified the Hague and Geneva conventions, which are universally accepted as customary international law, applicable to every situation of armed conflict in the world.

The four separate atrocity crimes have a long and significant history in international human rights law. Each crime has specific elements, and perpetrators might be guilty of one crime and not the others, or a perpetrator can be guilty of more than one crime and sentenced for each of those crimes. In addition, since multiple elements are contained within the definition of each crime, an accused person can be charged with several counts of a specific crime.

The mechanisms for justice

There are international, regional, and national mechanisms for holding perpetrators accountable for these four crimes, and teams of investigators and analysts have been in Ukraine since Russia’s invasion to prepare for trials.

One mechanism is the UN International Court of Justice (ICJ) in The Hague, Netherlands, also called the World Court. This court hears cases between states for disputes over broken treaties and international agreements. Almost immediately after the invasion, Ukraine filed a case against Russia at this court for violating the UN Genocide Convention, which both countries have ratified.23

A unique feature of this court is that other states can get involved in a particular case, and 14 states, including the U.S. and the entire European Union, have signed on with Ukraine against Russia over violations of the prevention of genocide.24

A second mechanism is the International Criminal Court (ICC), also in The Hague. The jurisdiction of the ICC is very different from the ICJ. The ICC only prosecutes individuals for the four core international crimes, and for incidents occurring from the year 2002 forward.25

The ICC opened cases against Ukraine on March 2, a week after the invasion began. Fully 43 states have referred cases to this court. The chief prosecutor of the ICC, Mr. Karim Khan of the UK, has visited Ukraine four times.26 He has announced that cases have been opened for war crimes, crimes against humanity, and genocide, committed on any part of the territory of Ukraine by any person from November 21, 2013, onwards, commencing with Russia’s invasion of the Crimea.27

The ICC issued its first arrest warrants for the situation in Ukraine on March 17, 2023, for Vladimir Putin and Maria Lvova-Belova, commissioner for children’s rights in the office of the president, for perpetrating war crimes in Ukraine.28 Putin and Lvova-Belova are charged with unlawfully deporting and transferring thousands of children from occupied areas of Ukraine to Russia. Children, including infants, have been abducted from orphanages, hospitals, summer camps, and other institutions primarily in the southern and eastern regions of Ukraine. Most of the abducted children have relatives who are desperately searching for them.

Russia appears to be taking the ICC warrants seriously. Dmitry Medvedev, former president of Russia and the current deputy head of Russia’s Security Council, warned that Russia could strike the ICC with a hypersonic missile in reprisal for the arrest warrant, and that attempts to try Putin at the ICC would have "monstrous" consequences for international law.29

On March 22, the Presidency of the Assembly of States Parties, which is the ICC’s administrative arm, issued a chilling press release that “reaffirmed its unwavering support for the International Criminal Court in the face of threats and measures announced against its Prosecutor and Judges involved in the issuance of arrest warrants in the Ukraine situation.”

The ICC is investigating potential cases of genocide and crimes against humanity in Ukraine as well as war crimes.

A third mechanism is through trials in Ukraine in domestic, or national, courts. Three months after Russia’s invasion, Ukrainian courts delivered the first convictions for war crimes committed by Russian soldiers.30 An estimated 70,000 war crimes are pending investigation in Ukraine right now.

Another mechanism is the use of universal jurisdiction, which allows crimes that are especially heinous to be prosecuted almost anywhere in the world, with the treaty basis for universal jurisdiction originating in the 1949 Geneva Conventions. The crimes under universal jurisdiction include the four core international crimes. National courts in a number of European countries are already bringing cases forward using this process.

Ukraine also brought a case against Russia in the European Court of Human Rights in Strasbourg, France, alleging a pattern of violations of the Articles of the European Convention on Human Rights dating from spring 2014. This court issued an interim verdict on January 25, 2023, “ruling partially admissible Ukraine’s allegations of Russia’s human rights violations in eastern Ukraine, setting a precedent as the first international court to prove Russia’s occupation in Donbas since 2014.”31 The ruling also set definitions for assessing Russia’s violations of human rights during its occupation, including:

  • shooting and torturing to death of civilians and Ukrainian prisoners of war;
  • torture, including sexual violence, rape, inhuman and degrading conditions of detention;
  • organizations of forced labor;
  • kidnapping, illegal arrests, and long-term illegal detention;
  • attacks on religious grounds;
  • persecution of journalists and blocking of Ukrainian broadcasters;
  • destruction and unlawful appropriation of private property;
  • bans on education in the Ukrainian language;
  • persecution of persons of Ukrainian nationality or citizens who supported the territorial integrity of Ukraine.

The court did not confirm the violations but declared that preliminarily evidence seems to be present.32

Another mechanism for ending impunity and advancing justice now exists in U.S. law. On December 22, 2022, Congress unanimously passed the Justice for Victims of War Crimes Act, which permits the prosecution of alleged war criminals who attempt to hide in safety in the U.S. regardless of the nationality of the perpetrator, the victim, or where the crime occurred, with no statute of limitation. The legislation was supported by the Departments of Justice, State, Defense, and by the White House. The bill passed just a few hours before Ukrainian President Volodymyr Zelensky addressed a joint session of Congress.33

The European Union announced on March 5, 2023, the creation of a new international tribunal to prosecute this crime of aggression. Although aggression is within the mandate of the International Criminal Court, it requires that Russia accept the jurisdiction of the ICC, which it does not. The EU has therefore established the International Centre for the Prosecution of Crimes of Aggression against Ukraine34 (ICPA) to fill this gap.


The various mechanisms described above pose the potential for investigators to duplicate efforts; use non-uniform practices; interview the same witnesses and victims multiple times using different criteria; employ varying standards for collecting, verifying, and analyzing evidence; and employ other practices that could limit the admissibility of materials in future court proceedings. In view of these obstacles, the U.S. and 45 other nations formed an umbrella group in July 2022 to standardize practices, train Ukrainian prosecutors, and expand the number of forensic teams in Ukraine to enable consistent and high-quality evidence-gathering for subsequent proceedings. The participating nations also pledged $20 million to assist the ICC, the UN support efforts, and the Ukrainian prosecutor general’s office, in unprecedented international investigatory teamwork.35

The US, the European Union, and the UK have formed the Atrocity Crimes Advisory Group36 (ACA), which consists of two key components: the Prosecutorial Support Unit (PSU) and Mobile Justice Teams (MJTs). “The PSU provides expert advice on international humanitarian law, guidance on the building of case files, expert opinions and overall direction on the prosecution of domestic cases. The MJTs serve a rapid response function by providing expert advice to Ukrainian investigators situated in the field.”

The United Nations Human Rights Council established the Independent International Commission of Inquiry on Ukraine on March 4, 2022, a week after Russia’s invasion, to investigate abuses of human rights, violations of international humanitarian law, and other possible crimes.37 Commission members visited 27 towns and settlements and interviewed more than 150 victim-survivors and witnesses. Investigators inspected sites of destruction, graves, and places of detention and torture. They met with government authorities, international organizations, civil society representatives, and other relevant stakeholders. The commission reported that war crimes and violations of human rights and international humanitarian law have been committed, and Russian armed forces are responsible for most of the violations.

A number of other entities are involved in investigations. The European Union Agency for Criminal Justice Cooperation, or Eurojust,38 is supporting the work of a joint investigation team (JIT). A JIT is the most advanced tool in international cooperation in criminal matters; it is composed of judges, prosecutors, and law enforcement officials working together on transnational investigations. JITs are operating on the ground throughout Ukraine.

On March 3, 2023, U.S. Attorney General Merrick Garland signed a memorandum of understanding (MoU) with the seven-nation JIT partners to pledge further cooperation and coordination in their respective investigations occurring in Ukraine.39

Another investigative mechanism is the Genocide Network, whose official name is the European Network for Investigation and Prosecution of Genocide, Crimes against Humanity, and War Crimes.40 The Genocide Network enhances cooperation between national authorities investigating these three core crimes, with a mandate to ensure that perpetrators do not have impunity within the European Union member states.

Finally, police networks support the work of Eurojust, the ICC, the JITs, and the Genocide Network. Europol,41 the European Police Office, is the European Union law enforcement organization handling criminal intelligence; the global entity is Interpol, the International Criminal Police Organization. The FBI operates in collaboration with both Europol and Interpol.

Europol is supporting investigations into war crimes through the Analysis Project: Core International Crimes (AP CIC) and an operational task force of experts to assist in war crimes investigations conducted by Ukraine, other countries, and ICC.


Russia’s invasion and occupation of the Donbas and Crimean regions in eastern Ukraine in 2014 set the stage for Russia’s all-out invasion on February 24, 2022, and the subsequent war has destabilized the entire world. Support for Ukrainians’ efforts to maintain democracy and independence from Russia has been swift, significant, and unprecedented, coming from individuals as well as national and global entities. But that support appears to be eroding as the war, and its concomitant economic, environmental, and social costs, continues with no end in sight.

The mechanisms to end impunity for the perpetrators of the four core international crimes are also unprecedented in both scope and support. It is hoped that both peace and justice can prevail.

ELLEN-KENNEDYELLEN J. KENNEDY, Ph.D., is the founder and executive director of World Without Genocide, a human rights organization located at Mitchell Hamline School of Law in St. Paul, where she is also an adjunct professor.









8 Estimates of the number of deported Ukrainian children to Russia range from 13,000 to 307,000, without any indication as to when they could return to their home cities. The Ukrainian Office of the Prosecutor General also claimed that nearly 800 children had died or disappeared in the process of deportation.





13; See Part 2.





18 Russia was not invited to join the League due to the radical policies of the new communist government. The Soviet Union finally became a member of the League in 1935. In November 1919, the U.S. Senate voted against accepting membership to the League, and the US never joined.,and%20the%20nation%20never%20joined.



























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