Editor's Note: (Ruti Teitel is Ernst C. Stiefel Professor of Comparative Law at New York Law School, co-director of the Center for International Law, and director of the Institute for Global Law, Justice, and Policy. She is the author of "Humanity's Law." The views expressed here are her own. Read more opinion on CNN.)
(CNN) Since Russia launched its invasion of Ukraine nearly six weeks ago, it has left a path of destruction -- and along the way, ignored the cardinal principle of the law of war.
By destroying Ukrainian cities and killing ordinary people, including children, Russia has failed to distinguish between military and civilian targets.
As a result, Ukraine has suffered more than 3,500 civilian casualties, including over 1,400 deaths, as of April 4, according to the Office of the UN High Commissioner for Human Rights.
Shocking images of bodies in the street have already emerged from places like Bucha, on Kyiv's outskirts. Ukrainian President Volodymyr Zelenksy warns the civilian toll will likely be much higher in other liberated cities.
As the horrors of Russian President Vladimir Putin's invasion become more apparent, how should Ukraine and the international community react to what may be war crimes and crimes against humanity? Here's a look at what actions can be taken.
No respect for humanitarian corridors
From the war's beginning, the invasion was highly indiscriminate, involving the shelling of Ukrainian cities. Russia's actions provoked widespread demands to protect citizens fleeing from the destruction.
In situations such as these, the UN Office for the Coordination of Humanitarian Affairs provides for what is known as a humanitarian corridor. Despite international agreement about these corridors, Russia has interfered, shooting at civilians and leaving roads littered with the dead and wounded.
Possible law of war violations reported
The law of war has long prohibited intentional attacks on civilians, called noncombatants, as well as attacks that do not distinguish between civilian and military targets.
A report this week by Human Rights Watch, based on interviews with eyewitnesses, victims and local residents of Russia-occupied territories between February 27 and March 14, documents many law of war violations. Interviewees described repeated rape and summary killings, as well as threats against civilians.
Some of these offenses, especially those coming to light in Bucha, may not only be war crimes but possess such gravity as to be considered crimes against humanity. Crimes against humanity involve the most serious crimes such as murder, torture and persecution aimed at civilians as a matter of widespread or systematic attack.
Where the courtroom comes into it
The International Criminal Court (ICC) is the institution perhaps most often mentioned as appropriate for the prosecution of these crimes. The ICC has jurisdiction over both a wide range of war crimes and crimes against humanity. It also has jurisdiction to prosecute genocide. The US is not a member of the ICC, despite its support for the court's prosecution of other countries' leaders and military.
But neither Ukraine nor Russia is a party to the Rome Statute -- essentially the constitution of the ICC. Though not a party, Ukraine has voluntarily accepted the jurisdiction of the ICC on an ad hoc basis over crimes committed on its territory. This allows the ICC to investigate, and where appropriate, prosecute any of the crimes listed in the Rome Statute that take place, in whole or in part, on Ukrainian soil.
This applies whether the accused are Russian or Ukrainian nationals, or nationals of a third state (for example, mercenaries from Syria).
Also, the accused need not be present on Ukraine territory. That means leaders and commanders may commit war crimes or crimes against humanity -- so-called command or leader responsibility -- even if they never set foot on the battlefield.
It all depends on whether these atrocities can be traced to their direct orders, or in some cases even willful blindness or failure to prevent anticipated offenses.
Even Putin could be prosecuted -- one of the features of the ICC is that a head of government or head of state has no immunity. Of course, bringing Putin or other Russian commanders before the ICC in the Hague involves formidable challenges at a practical level. The ICC does not permit "trials in absentia" where the defendant is not present and it seems unlikely that Putin would fall into the court's custody any time soon.
There could also be domestic prosecutions
Right now, Ukraine's own prosecutors and other criminal justice officials are collecting evidence concerning war crimes and crimes against humanity in Ukraine. In fact, the ICC operates on the basis of "complementarity" -- it will only prosecute in situations where Ukraine is unwilling or unable.
Russian or other prisoners of war captured by Ukrainian forces may be tried for specific war crimes or crimes against humanity. But they cannot be prosecuted merely for fighting in the war.
The fact that Ukraine is preparing to prosecute Russian war crimes potentially signals the standards by which it is ready to hold its own army to account, as committing its own war crimes would open Ukraine up to "tu quoque" -- the possible accusations that they, too, have lacked integrity in their military tactics.
Other countries are also ready to prosecute
Other countries could prosecute by exercising "universality jurisdiction" -- using domestic legislation to prosecute war crimes, even if they were not committed on their territory, by or against their citizens.
Historically there have always been crimes -- such as piracy -- that are considered offenses to all humanity. There is widespread agreement that the crimes set out by the ICC as worthy of prosecution are punishable offenses.
For example, Germany has just announced an investigation into Russian aggression against Ukraine. There's already a track record here as Germany has prosecuted crimes against humanity vis a vis Syria where convictions have already been secured. In January, a German court sentenced former Syrian army colonel Anwar Raslan to life in prison for crimes against humanity, after he oversaw the torture of detainees a decade earlier.
The many groups investigating war crimes
After the apparent massacres of civilians in Bucha and other sites of Russian withdrawal, there has been a steady drumbeat from the White House, NATO, the EU and other international leaders all calling for accountability. In this spirit, a team of international prosecutors has been convened by the US State Department to go to the region to assist the Ukrainian Procurator General's office to gather evidence of war crimes.
Shortly after the Russian invasion began in February, Karim Khan, Prosecutor of the International Criminal Court, also announced that he would open an investigation into alleged atrocities; expanding an investigation originally dating back to Russia's 2014 invasion.
And earlier this month, the United Nations Human Rights Council established an Independent International Commission of Inquiry, to investigate alleged violations of human rights in Ukraine.
Of course, many human rights organizations, such as Human Rights Watch and Amnesty International are also gathering evidence, as are countless journalists.
Despite the challenges of judging crimes during wartime, it's necessary for peace
What trials could do is underscore individual responsibility for brutality in war -- contributing to the road to peace.
There are fairly recent precedents to this. During the 1990s, in the last war in Europe following the collapse of Yugoslavia, we saw the United Nations Security Council establish the International Criminal Tribunal for the Former Yugoslavia (ICTY) -- an intra-war tribunal to adjudicate war crimes, crimes against humanity and genocide during the bloody Balkans conflict.
The court was aimed at peacemaking -- to deter and end the violence. The international tribunal's mandate was to indict those responsible for "ethnic cleansing" throughout the region, including ultimately top political and military leaders in the conflict.
Leading political and military officials of the regional conflict -- including Slobodan Milosevic, Radovan Karadzic and General Radko Mladic -- were prosecuted at the ICTY. Slobodan died during pendency of the trial, while Karadzic and Mladic were convicted in 2016 and 2017 and are currently serving long sentences.
Then-Secretary of State Madeline Albright said at the time "the only victor that will prevail in this endeavor will be the truth."
Likewise, in the words of the first ICTY prosecutor Richard Goldstone who justified the indictments in terms of the truth and deterrence, "the public record will assist in attributing guilt to individuals and be an important tool in avoiding the attribution of collective guilt to any nation or ethnic group."
Given ongoing Russian denials of war crimes (including recently of the Bucha massacre) and even of the invasion of Ukraine (calling it an "operation"), trials and establishing a criminal record could go a long way in stopping the nationalist propaganda which has promoted cycles of violence in the region.
As the ICTY showed, international justice can be an ally in negotiating peace. Let's hope that justice for Ukraine follows in the footsteps of other tribunals during war and advances peace in the region.