Ukraine and its backers on Friday gave the green light to setting up a special tribunal to try Russia's top leadership for the "crime of aggression."But what does this mean and how will it work?Here is what to know about the tribunal:Why is this tribunal needed?Ukraine and its supporters want to see justice served for Russia's all-out invasion in 2022.The International Criminal Court (ICC) in The Hague has already issued arrest warrants for President Vladimir Putin over the abduction of Ukrainian children, and four of his top commanders for targeting civilians.But the ICC does not have the jurisdiction to prosecute Russia for the more fundamental decision to launch the invasion otherwise known as the "crime of aggression."This new tribunal seeks to close that loophole and focuses on trying to hold the top roughly 20 to 30 officials in Russia responsible for the all-out assault."This has to convey the message that there is no impunity for such grave violations of international law, and the crime of aggression is the mother of all," an EU official said.Will Putin be tried?Putin won't face trialfor as long as he remains in office under a principle in international law granting the so-called "troika" of president, prime minister and foreign minister immunity.But prosecutors from the court can still draw up an indictment for the Russian leader, which would then be put on hold by judges until he is no longer president.The other suspects beyond the "troika" could meanwhile face trial, including in absentia if they are not handed over to the court.Anyone found guilty could face up to life imprisonment and have their assets confiscated and used to pay reparations to Ukraine.How will it work?Experts from Ukraine and the roughly 35 other countries involved have spent some two years wrangling over the legal details of how a tribunal would work.Officially, the court will be established under the auspices of the Council of Europe the continent's top human rights body.Investigators from Ukraine and six EU member states have begun work and collected a wealth of evidence already.Officials say they hope the tribunal will be formally established early next year and once it is the cases will be transferred to prosecutors at the court.The location of the tribunal is still to be decided, but likely destinations include The Hague or the home of the Council of Europe in Strasbourg.Is the United States involved?The United States was a key player in pushing talks on setting up the court under former President Joe Biden.That has changed since Donald Trump returned to the White House, and there was no representative from Washington present for the endorsement in Lviv.Trump is not a fan of efforts for international justice and has threatened the ICC over its arrest warrant for Israeli Prime Minister Benjamin Netanyahu.But his comeback appears to have sped up the creation of the tribunal, as European officials fear his push for a peace deal could mean Moscow escapes justice for good.Ukraine and its backers insist that there should not be impunity for Putin and his cronies under any deal to end the war.