Mr. Maduro immediately blamed a prominent opposition leader, Leopoldo López, for the violence and ordered him arrested, saying that he had trained young people to spread violence during the protests as part of a conspiracy to topple his government. Mr. López turned himself in last week, and he was charged with inciting violence. He has denied the accusations and called for peaceful protests.

The protests, fueled by economic problems, high crime and dissatisfaction with the government’s socialist-inspired policies, continued on Wednesday. Government supporters also marched in several cities.

But the arrests announced on Wednesday appeared also to be linked to broader questions around the intelligence service.

Within days of the killings, Mr. Maduro announced that members of the service had disobeyed an order to stay off the streets during the protest. He also said that men in Sebin uniforms had been seen lurking around Mr. López’s home, although there was no order for them to go there, and he warned of a plot to murder Mr. López.

Soon after that, he reassigned the head of the service, who had been on the job only a few weeks. He also hinted that if members of the intelligence service had been present at the march, they might have been part of a conspiracy against the government.

All that has watchers of the conspiracy-minded Mr. Maduro alert to possible hidden meanings in the prosecutor’s moves.

“This is going to be a novel in installments,” said José Vicente Haro, a constitutional lawyer close to the opposition. “We get one chapter today, another the next day, another the next day and so on until we can decipher the answer to the mystery, in the best style of Agatha Christie.”