The music has been switched off at the Red Light pub in the heart of the picturesque old town of Gdańsk. A single candle adorned with a black ribbon rests on the bar. The city is in mourning.

The people of Gdańsk are coming to terms with the death of their mayor, Paweł Adamowicz, who was stabbed on stage at a charity concert in front of thousands of people on Sunday. A public appeal led to crowds of people queueing for hours to donate blood to save their mayor, but he was pronounced dead on Monday afternoon.

At the Red Light, people console each other between shots dedicated to Adamowicz. Adela Szczepańska-Kościelnik was at the concert when the attack happened. It was the local finale of a nationwide charity drive, the Great Orchestra of Christmas Charity, which raises funds to buy equipment for children’s units in state-run hospitals. The concerts end with a countdown towards the moment when fundraising stops and people raise lights in the air in celebration. Adamowicz was leading the countdown; the attack was timed to coincide with the moment it reached zero.

“At the end of the countdown we didn’t understand what happened. There was no light, no music. A girl started screaming: ‘They killed him! They killed him!’ We were confused, some people thought it was a joke. The city has never been so sad, it is as if someone cut the electricity.”

Play Video 1:02 Thousands across Poland pay tribute to stabbed Gdańsk mayor - video

After the announcement of the mayor’s death on Monday, thousands of people gathered at the statue of Neptune in the city’s Long Market, also home to city hall, where Adamowicz served for more than 20 years. With tears running down people’s faces, the crowd stood motionless as they listened to an a capella version of Simon and Garfunkel’s Sound of Silence.

This was silence with a purpose – not only to mourn, but to protest against an increasing prevalence of hate speech in Polish public discourse that Adamowicz had attempted to confront. A staunch defender of migrants and refugees and of LGBT rights, he had marketed Gdańsk as a liberal enclave, a city in open defiance of the xenophobic nationalism promoted by Poland’s rightwing Law and Justice party (PiS), which has governed since 2015.

“I am a European so my nature is to be open,” Adamowicz told the Guardian in 2016. “Gdańsk is a port and must always be a refuge from the sea.”

His liberal stance cast him as a hate figure for government supporters and the far right. In a 2017 publicity stunt, the All-Polish Youth movement published a series of “political death certificates” of pro-European politicians; on Adamowicz’s certificate, they put his “cause of death” as “liberalism, multiculturalism, stupidity”. Observers say he was regularly subjected to personal attacks and abuse on social media and from rightwing media outlets.

Facebook Twitter Pinterest Demonstrators holding a ‘stop the hate’ banner during a march in memory of Paweł Adamowicz on Monday. Photograph: Attila Husejnow/Sopa Images/Rex/Shutterstock

Some of the attacks continued even after he died. In an interview with a rightwing media outlet broadcast on the day Adamowicz’s death was announced, the far-right politician Grzegorz Braun described him as a “traitor to the nation” for his political views.

“Sadly, hatred is becoming more and more visible and more widely accepted in Polish political and social life,” read a joint declaration of Jewish organisations in Poland, published on Tuesday. “The death of Mayor Paweł Adamowicz is yet another tragic warning signal that in our society, ideological differences, and differences of worldview, can lead – in extreme cases – to acts of physical violence.”

Adamowicz told the Italian newspaper la Repubblica in 2017: “Physical abuse is normally preceded by verbal violence. When the language of the elites violates the limits imposed by decency, it causes more and more physical violence. Unfortunately this is not a theory but the reality, as the growing cases of racially and religiously based violence demonstrate.”

Some people have drawn parallels between Adamowicz’s murder and the assassination of Gabriel Narutowicz, the leftwing president of interwar Poland who was shot by a rightwing activist in the 1920s. Making this connection explicit, a silent “march against hatred” held in Warsaw on Monday evening made its way through the streets of the capital to the Zachęta art gallery, where Narutowicz was killed in 1922.

Facebook Twitter Pinterest A woman signs a book of condolence for Paweł Adamowicz in Warsaw on Tuesday. Photograph: Tomasz Gzell/EPA

Many on the Polish right have accused their liberal opponents of politicising the murder by attributing political motives to the killing. The alleged murderer, a 27-year-old resident of Gdańsk named in press reports as “Stefan W”, said he had been released from prison only last month after serving a jail sentence for a series of violent bank robberies. According to Polish media reports, he was diagnosed with and treated for paranoid schizophrenia while in prison, but stopped taking his medication before his release. He pleaded not guilty to murder on Monday.

Many of Adamowicz’s supporters, noting he has long been a target of aggressive government propaganda, are incensed at what they regard as attempts by those they hold largely responsible for Poland’s toxic political climate to wash their hands of any responsibility.

“If you watched our main government TV, you would see that for months there were programmes about how bad he is, how he lies, how he steals,” said Witek Nabożny, a resident of Gdańsk who had come to the statue of Neptune to pay his respects. “They created a mood in which weak people, sick people, respond to this kind of atmosphere.”

“Adamowicz has become a symbol of something bigger than the attack itself. He died during a charity event that tries to bring Poles together. As a result, he became a symbol of the death of unity in this society,” said Rafał Pankowski, the director of the Never Again association, an anti-racism campaign group. Adamowicz had begun his career as a much more conservative politician, he said.

“He started to become more and more outspoken on issues of diversity and minority rights and tolerance just as society was moving in the opposite direction. It was very impressive. He was a very brave man – and he paid for it.”