After an attack in April on a camp in Lysa Hora park outside Kiev, when a nationalist group threw rocks, squirted pepper spray and burned down tents, it seemed like an outbreak of the old ethnic scourge, and the episode drew criticism from Western governments and rights groups.

The Ukrainian government seemed to see the assault differently, at least at first. Far from prosecuting the nationalist group, known as C14, which filmed the attack and posted photographs on the internet, the government gave it a state grant in the form of free rent for auditoriums to support “patriotic education.”

Image Yevhen Karas, the leader of a nationalist group called C14, in Kiev in June. “We were called fascists,” he said, referring to the reaction to his group’s attack on a Roma camp in April. But, he added, “I do not care what they call us.” Credit... Genya Savilov/Agence France-Presse — Getty Images

No arrests were made immediately after the April attack. Soon enough, five other major assaults ensued, along with dozens of smaller episodes. After one nationalist group, called Sober and Angry Youth, killed a Roma man, David Pap, last month in Lviv, the police detained suspects. Nothing had been done against this group earlier, though it had posted a video online of its members chasing Roma through the city in “A Safari on the Gypsy.”

In July, a court sentenced one participant in the April attack to two months of house arrest.

“No group has the barbaric right to do what was done,” the interior minister, Arsen Avakov, said after the killing in Lviv. Mr. Avakov said the police would act “even if these people cover themselves with the status of veterans.”