Police released security footage of a man in a dark shirt walking to the New Synagogue in Gdansk, Poland, and throwing a stone into a window during Yom Kippur services.

Authorities appealed to anybody who recognizes the man to contact police.

The city’s mayor, Pawel Adamowicz,  said he was “appalled,” especially because it took place during the prayers of Yom Kippur. “Such things should not happen in the city of freedom and solidarity,” he said.

He called on residents to gather on Thursday evening outside the synagogue in a show of protest.

The World Jewish Congress strongly condemned the “shocking and dismaying” attack on the synagogue.

“We trust that the local police authorities in Gdansk are investigating this matter with the diligence it deserves, and that the perpetrators of this cowardly act will be swiftly brought to justice,’’ said WJC president Ronald S. Lauder. “In recent years, Jews in Poland have been able to worship with a sense of security, and we hope that this attack does not herald negative change in that positive environment.”