Lenny Goldberg, the father of the bride whose wedding was shown in the video, implied that the leaking of the video served the interests of security agencies. “Public opinion was against the G.S.S.,” Mr. Goldberg told Israeli news outlets, referring to the General Security Service, another name for the Shin Bet, “and then the wedding made kosher what they want to do.”

The Shin Bet hinted at harsher than usual interrogation methods in a statement it issued on Thursday, but it rejected allegations of abuse and said the investigation was taking place under close judicial supervision.

The video, much like the arson attack itself, prompted shock and outrage. “You disgrace your skullcap, your prayer shawl and the name of God,” news reports quoted Isaac Herzog, head of the political opposition in Parliament, as saying on social media. “Whoever dances at a wedding and celebrates the murder of a sleeping baby is not Jewish and not Israeli.”

Israeli news media reported that Defense Minister Moshe Yaalon summoned advocates for Jewish settlements in the West Bank to his office to show them the video, apparently to impress upon them the seriousness of the extremists who have emerged at the movement’s fringes.

“I look into my past, not just my military past, but my past as a settler, as a teacher, and wonder if I did not do enough so that there would never be such sights,” said Rabbi Avihai Ronsky, the head of a yeshiva in the Jewish West Bank settlement of Itamar. Still, he said, the extremist Jewish fringe consists of “a very small handful of people.”

Palestinians and their supporters say the arson attack and the celebratory video were inevitable, complaining that the Israeli authorities have for years dragged their feet on finding and prosecuting extremist Jews who have physically attacked them and their property.