BRUSSELS (WASHINGTON POST) - A prominent Polish opposition leader, Gdansk Mayor Pawel Adamowicz, died Monday (Jan 14) after being stabbed in the chest a day earlier at a charity concert, unsettling Polish politics at a tense and polarised moment in the nation's history.

The attack, which was broadly condemned across the political spectrum, stunned a country that has become deeply divided over attempts by the ruling Law and Justice party to increase its control over courts, media and other aspects of public life.

Polish authorities said the alleged assailant was a 27-year-old man with a history of crime and mental illness.

After he stabbed Adamowicz repeatedly on a stage in front of crowd of thousands, he declared himself to have been wrongfully imprisoned by the Poland's previous ruling party, which had supported Adamowicz.

The mayor of a Polish city famed for its independent-minded shipworkers who played a critical role in the fall of Communism, Adamowicz was known for his pro-migration views, support for gay rights and his efforts to fight attempts by Poland's ruling party to bolster its power over the country's judiciary.

Those issues cut across the grain in a country increasingly dominated by Law and Justice, even as national leaders moved quickly to support the mayor and his family.

"Hostility and violence has brought about the most tragic and painful result," wrote Polish President Andrej Duda on Twitter, a day after he wrote that "we usually disagree with Mayor Pawel Adamowicz in political views about how Poland should be governed, but today we are with him and his family unconditionally".

The Polish government sent a plane to London to bring home Adamowicz's wife, who was in Britain at the time of the attack.

Polish authorities, who identified the suspect only as Slawomir W., said he had been released from prison recently after serving more than five years for committing a string of bank robberies. They said he had used a press pass to get onto the stage and were investigating how he had obtained it.

Whether the attack was politically motivated was not immediately clear.

But Adamowicz's allies said it was difficult to separate the crime from a broader context of anger, hate speech and calls to violence that has been on the rise in Poland in the three years since Law and Justice took office.

Some said they feared the country could become even more split in the aftermath of the murder.

Last year, the far-right All-Polish Youth organisation issued fake death certificates for 11 opposition politicians, including Adamowicz, ahead of October local elections. Human rights advocates asked prosecutors to press charges, but authorities said the death certificates comprised legitimate political speech.

"In the upcoming days we need to do everything possible in order to save our humanity and in order to save what is good in our society," Polish Human Rights Commissioner Adam Bodnar said Monday.

Bodnar, who teamed with the mayor on different issues during Adamowicz's 20-year tenure leading Gdansk, said he was trying to be careful not to point fingers before the motivations behind the crime are known. But he said that it was hard not to think about the broader context.

"I am trying to be very responsible about what I am talking about," he said.

"If we talk about general trends, then yes, the government and especially the prosecutors' office was not doing enough to combat hate speech. When I see this death certificate with his face which was made by right-wing NGOs, what am I supposed to think?"

Even before Adamowicz was pronounced dead Monday afternoon, Polish civic groups had planned to hold rallies against hate speech Monday in Warsaw, Gdansk and elsewhere around the country, and they turned into impromptu memorials for the slain mayor. Duda, the Polish president, announced Monday that he would hold an anti-violence rally on Tuesday.

But some people questioned whether the government had done too little to fight calls for violence.

"You could easily imagine a person who would have done the same having been much more motivated by the context in which it happened," said Piotr Buras, the head of the Warsaw office of the European Council on Foreign Relations, a think tank.

"That's, for me, the bottom line, and that's why it is for me a warning that if you tolerate this level of hatred in the public debate, much can happen."