Poles place candles and flags at half-staff for slain mayor Flags flew at half-staff and people signed condolence book at municipal buildings across Poland as the nation mourned the long-serving mayor of Gdansk by an ex-convict with a grudge against the politician's former political party

WARSAW, Poland -- Flags flew at half-staff and people signed condolence books at municipal buildings across Poland and in diplomatic missions abroad on Tuesday as the nation mourned the stabbing death of the popular liberal mayor of Gdansk.

Meanwhile, Interior Minister Joachim Brudzinski said police have arrested three people who had called for more killings following the assassination of Pawel Adamowicz, who died Monday after being stabbed the previous day during a charity event.

Brudzinski described those arrested as internet trolls and as mentally disturbed. Police reported that the threats were directed against the country's president and other city mayors.

In Gdansk, a historically rich city on the Baltic Sea, people placed flowers and candles and signed a condolence book at the town hall, where Adamowicz had had his office since he was first elected mayor in 1998.

In the capital, Warsaw, Prime Minister Mateusz Morawiecki and members of his Cabinet stood for a moment of silence in Adamowicz's honor before their weekly meeting.

The assailant stabbed Adamowicz three times in the heart and abdomen while on stage during a charity event Sunday evening. He then told a crowd of thousands he did it in revenge against the opposition Civic Platform party, which was in power when he was imprisoned in 2013 for bank robberies.

Adamowicz was a longtime member of Civic Platform but left it in 2015.

Officials have identified the assailant as 27-year-old Stefan W. from Gdansk who left prison in December after serving more than five years. Justice officials said he needed psychiatric examination and that a psychiatrist assisted at his questioning Monday.

The killing plunged the politically divided country into shock and grief and brought Poles into the streets for solemn vigils Monday night. In one particularly emotional moment, a huge crowd at Gdansk's old town square fell silent as an intense and heartrending version of the song "Sound of Silence" sung by American hard rock band Disturbed played out, some wiping away tears.

Some Poles put some of the blame for the assassination on the right-wing ruling Law and Justice party, which has often employed harsh language to denounce its critics, among them Adamowicz. They accuse it of creating a climate of intolerance and eroding democratic standards. They have primarily focused their criticism on the party's reshaping of the judicial system and its use of public media as a political tool.

Government officials and some independent observers called for caution, noting the assailant's criminal record and suspected psychiatric problems.

Amid the recriminations, state broadcaster TVP ran a report on its main evening news program Monday that selectively showed clips of officials with Civic Platform using harsh language against Law and Justice over the years. Critics noted that it left out the many examples of verbal aggression by Law and Justice officials, creating an impression that Civic Platform is solely responsible for the rising level of animosity in the country.

Jaroslaw Olechowski, head of the news program, tried to refute the criticism, saying on Twitter that the only criterion in selecting the quotes were words "calling for physical violence." Critics pointed out that violent remarks by ruling party officials and members were not used in the report.

Wladyslaw Kosiniak-Kamysz, the head of the small opposition Polish People's Party, called on the ruling party leader Jaroslaw Kaczynski to immediately fire the head of TVP, saying its flagship evening news broadcast was "generating mutual hatred" and destroying national solidarity.

A petition addressed to Kaczynski garnered thousands of signatures Tuesday.

Adamowicz was part of the democratic opposition formed in Gdansk under the leadership of Lech Walesa during the 1980s. After leaving Civic Platform, he was re-elected to a sixth term as an independent candidate last fall.

For years, he was denounced by members of Law and Justice and some further to the right, who accused him of lacking patriotism or promoting degenerate values with his liberal views.

As mayor, he was a progressive voice, promoting tolerance for LGBT people and minorities. He showed solidarity with the Jewish community when the Gdansk synagogue had its windows broken last year, strongly denouncing the vandalism. He had also advocated bringing wounded Syrian children to Gdansk for medical treatment, but the plan was blocked by the Law and Justice government.

The American Jewish Committee and other Jewish organizations in Poland issued a joint statement Tuesday saying they were "stunned in disbelief" at the killing of a man who had supported tolerance and diversity.

"A man who became one of the symbols of opposition against racial and religious prejudices in Poland, himself became a victim of hatred," the statement said.