In 2016, Burundi announced it would leave the International Criminal Court, and a wave of other African nations threatened to do the same. Burundi completed the withdrawal last year — and under the new constitution, it will be illegal to extradite Burundians accused of crimes.

Ms. Bouka sees other countries in the region, like the Democratic Republic of Congo, following Mr. Nkurunziza’s lead. Congo’s president, Joseph Kabila, also refused to leave office at the end of his second term, and his prolonged stay — and the country’s lack of elections — has created a political crisis, with pockets of violence across the country.

“I think people have said, ‘If Burundi can get away with this, so can we,’” Ms. Bouka said.

The lesson, she added, is clear: “If you can control the narrative — the diplomatic one, not the human rights one — you can ask how messy can things get without anybody forcing an intervention on you.”

Mr. Nkurunziza has tried to control the human rights narrative, too, by blocking access to journalists and researchers, including a United Nations Commission of Inquiry into accusations of extrajudicial killings, disappearances and torture since 2015, when Mr. Nkurunziza won his third term.

On voting day, many people in the capital, Bujumbura, and in the countryside said they were afraid of sharing their opinions openly, and some would speak only anonymously. Fears focused mainly on members of the imbonerakure, the youth wing of the governing party that the United Nations has accused of atrocities.

The young people lead security patrols in their neighborhoods, and on the eve of the vote, several groups could be spotted along the road north, toward the president’s stronghold. Most carried long wooden sticks, and a few machetes gleamed in the headlights of the rare oncoming car.

Almost no foreign journalists were given permission to report on the referendum, and ahead of the vote, the government blocked broadcasts by the BBC and Voice of America. Many local journalists have fled, and one reporter, Jean Bigirimana of the independent daily newspaper Iwacu, has been missing for nearly two years.