A spokesperson for the Warsaw prosecutors office, Magdalena Sowa, told reporters on Monday that an investigation had been launched into the "public propagation of fascism and calls for hatred" during the march on November 11, Poland's Independence Day.
The investigation will focus on the march's organizers and those who carried offensive banners, she said.
It remains to be seen if the move by the prosecutor's office indicates another step in the ongoing standoff between the Law and Justice (PiS)-led executive and a nominally independent judiciary, or perhaps an indication that PiS itself is genuinely politically worried by the strength of the far-right.
Participants chanted "Poland is all white!" and carried banners daubed with slogans such as "Death to enemies of the homeland!"
Police have reportedly been looking at recordings of the march and analyzing other evidence sent to prosecutors.
Police spokesman Mariusz Ciarka told reporters that in some cases the police had found violations of the criminal code. The offenses carry up to two years in prison.
Back to the future
Organizers of the march included the National-Radical Camp (ONR), the successor to a pre-war Polish fascist movement, the All-Polish Youth, a far-right youth organization that runs social media campaigns condemned as racist, and the National Movement.
Even more hard-line white supremacist groups, such as the National-Socialist Congress and the so-called Szturmowcy ("Stormtroopers"), were also present.
The march — under the slogan "We Want God" — was attended by some 30,000 people, according to data provided by the Warsaw city hall. Police estimated the crowd to be as many as 60,000 people.
The march has since been condemned by the European Parliament and Polish President Andrzej Duda.
Rise of Polish nationalism
The ruling Law and Justice party has been vocal in its antipathy towards immigrants, but quiet on the rise in xenophobia in Poland.
Some have argued PiS is trying to avoid a situation where the nationalists can gain a political — perhaps electoral — foothold to the party's right, a situation that some see as happening in Hungary with the ruling Fidesz and far-right Jobbik.
Others see this as a sop to the far-right.
"One could trace the origins of today to the rise of Polish nationalism, that is the Endecja [National Democrats], in the 1890s," political scientist Michael Steinlauf told DW.
"There is stunning continuity from then to now," he said. "There is a straight line through the interwar period, the war, communism and after. This continuity is the most amazing aspect of modern Polish politics. The interwar ONR [the quasi-fascistic National-Radical Camp] is back."
While the far-right remains a marginal feature of public life in Poland, in the absence of an effective opposition to euroskeptic PiS, its calls to arms find people willing to answer by taking to the streets and — as has been seen in recent years — pushing the line between populist rhetoric and far-right violence.
Since their inception in 2009, most Independence Day marches have descended into violent standoffs with the police and far-left groups.
Old hatreds, new foes
Rafal Pankowski, deputy editor of the Nigdy Wiecej ("Never Again") magazine and a lecturer at Collegium Civitas in Warsaw, said there has been a noticeable change in the political and discursive climate.
"It has become so much easier for people to say things they would never have said openly over the last 25 years," he said.
The European Jewish Congress expressed "grave concerns" in August over an increase in anti-Semitic acts in Poland, while a report by the University of Warsaw's Center for Research on Prejudice found that 37 percent of those surveyed voiced negative attitudes towards Jews in 2016.
"It is no coincidence that growing anti-immigration, anti-Muslim and generally xenophobic sentiment has been accompanied by a rise in anti-Semitic attitudes and behaviors," Robert Blobaum, author of "Anti-Semitism and Its Opponents in Modern Poland," told DW.
PiS's refusal to take in refugees has in turn triggered the regurgitation of some old tropes in the Western media, some rehashing the perennial accusations of Polish racism, others the peripheral, backward, "wild" East, others the simple ingratitude of it, after EU funds start to dry up.
An article in this week's Guardian newspaper, however, showed a more complex picture of a marginal movement hoping to seize opportunities provided by the success of the PiS and popular opposition to immigration from Muslim-majority countries.
There are "more girls, fewer skinheads" and an increase in middle-aged and highly educated recruits, the piece noted.
jbh/cmk (AP, AFP)