What constitutes a (prosecutable) war criminal

I’m asking mostly in regards to Putin (Russia invading Ukraine). He has given varying reasons why he ordered the invasion. None seem (to me) to rise to justification levels.

The US estimates between civilians and troops, over 60,000 Ukrainians have died so far. that’s a lot of people and doesn’t include Russians.

Could Putin be considered a war criminal? I realize we or the UN doesn’t have the wherewithal go and bring him to trial should we consider him so, but does he meet the definition? Is there an accepted definition?

I certainly consider him to be a war criminal. My problem, which seems to be the same as the rest of the world’s problem, is gaining access to prosecute and punish him.

The International Criminal Court has issued an arrest warrant for him, in March of this year, for war crimes, most specifically the forced deportation of children (which he denied, but later I seem to recall he bragged about it. I might be wrong about that). Russia does not recognize the jurisdiction of this court. For that matter, neither does the US. Ukraine has proposed seating a new tribunal, but I don’t think much has come of it. The ICC does, I believe, have a definition of war crimes and/or crimes against humanity, a definition that Putin appears to fulfill.

The Nuremburg trials only happened after the Allied victory and Nazi leaders had either been caught or killed. We are not in that situation yet, and we may never be. Remember Kaiser Wilhelm II, who bore significant responsibility for WWI and some German troop atrocities, was allowed to retire and die peacefully in, I believe, the Netherlands. It’s all a matter of military power, and how the victors intend to use it for what (I hope) is the best future for the countries involved. At least Putin can’t travel to a lot of countries himself, for fear of being arrested.

AFAICT, “war crime” is defined in the Rome Statute of 2002, which established the current International Criminal Court.

Putin is already considered (and charged) as a war criminal, in connection to his command responsibility towards specifc acts which violated Rome Statute Article 12 (as listed above):

Note that starting a war, no matter how egregious or evil, is not technically a war crime. The Rome Statute defines “crimes of aggression” separately from “war crimes”, and the ICC only has jurisdiction if the aggressor state accepts it.

That does rather sound like the winners get to decide what is a crime.
Have countries that did not sign the Geneva Convention been held responsible for not abiding by it?

Prosecutions of war crimes have historically been characterized by some as “victor’s justice”. Still, both parties in a conflict should be able to level charges at each other, whether winning or losing, if there is evidence of chargeable offenses. The only time a party would be completely unable to gain justice would be if they lose so thoroughly they don’t have a functional government or legal apparatus to convey the charges or represent the state at the ICC.

No one prosecutes people with access to nuclear weapons.

Well, presumably if he was in court, he couldn’t reach the button.