Reconciliation and forgiveness are often difficult to achieve.

Serbia’s Prime Minister Aleksandar Vucic had a brutal reminder of that Saturday. As he walked into a ceremony, a memorial honoring 8,000 Bosnian Muslims killed by Christian Serbs in Srebrenica, he was met by a crowd seething with anger and leading boisterous chants.

Tens of thousands came to mark the 20th anniversary of what’s been described as Europe’s worst massacre since the Holocaust.

As the premier prepared to lay down flowers, some in the crowd pelted him with stones and loudly whistled and booed. A scuffle broke out, and Prime Minister Vucic fled what the foreign ministry called an assassination attempt, reported The Associated Press.

But Vucic sought to downplay the attack. "Today we are talking more about a bunch of fools rather than about the innocent victims of Srebrenica," he said.

He added that his "arms of reconciliation remain stretched toward the Bosniaks."

War crime survivors often approach reconciliation in dramatically different ways, but this plurality shares a determination that the sacrifices of their loved ones are not forgotten, even if those who committed the crimes are forgiven.

Some survivors, like those among the millions victimized by the Japanese military during World War II, seek for decades an official apology from national leaders. Others, like Holocaust survivor Eva Kor, make waves in their communities for deciding to forgive their perpetrators. And those remaining, like the generations of modern Armenians who continue to demand recognition for the 1.5 million massacred 100 years ago, say they just want acknowledgment.

So how do leaders from the perpetrating countries – if ever – move forward?

Prime Minister Vucic was one of several foreign dignitaries who attended Saturday's event, including former President Bill Clinton, Turkish Prime Minister Ahmet Davutoglu, Britain’s Princess Anne, and Jordan’s Queen Noor, according to the AP.

Mr. Clinton said before the attack on Vucic: "I want to thank the prime minister of Serbia for having the courage to come here today and I think it is important that we acknowledge that."

Some in the crowd Saturday may have been incensed by the fact that Vucic's government got support from its ally Russia on Wednesday to veto a UN resolution calling the events in Srebrenica a genocide.

Upon arriving in Srebrenica, the BBC reports, Vucic published an open letter which did not use the word genocide, but said: "Serbia clearly and unambiguously condemns this horrible crime and is disgusted with all those who took part in it and will continue to bring them to justice."

The violent response to his presence at the memorial suggests that when people look at Vucic, they see him only in the past – and not the man who in recent years has repainted his image from a nationalist hardliner to a moderate, pro-Europe “right-of-center leader,” reports The Economist.

Vucic – who himself was not reported to have any injuries, but whose aide took a rock to the face – was instead reproached by the public for his role in the Bosnian War 20 years ago. People waved banners citing an inflammatory quote Vucic had blared as secretary-general of the extreme nationalist Serbian Radical Party known as SRS: “For every killed Serb, we will kill 100 Bosniaks.”

Since becoming prime minister, Vucic has made several attempts at reconciliation, including addressing a Jasenovac genocide memorial ceremony onsite of the former execution camp.

“The Serb people wish to make it clear at this place that they will not agree to death, that they will protect their homeland and kin and fight for life without the wish to take revenge, but they will never forget the past either,” he said, reported local news outlet B92.

He may have to keep trying.

“Look at him and look at those thousands of tombstones,” Hamida Dzanovic, who had come to Saturday’s Srebrenica memorial to bury bones identified as those of her missing husband, said to the AP. “Is he not ashamed to say that this was not genocide? Is he not ashamed to come here?”

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But in these situations, remembrance can often serve as a powerful tool, Michael Blumenthal, a German-Jewish Holocaust refugee and former U.S. Treasury Secretary, told the AP in 2001. One of the reasons that the Jewish sentiment of shunning Germany has diminished, he said, is that they recognize commemoration as an effective form of atonement.

“The German generation in power today is trying very hard to make amends,” said Mr. Blumenthal, founding director of the national Jewish Museum in Berlin. “They recognize that the worst thing that could happen is to forget.”