Tunisia's government says a leading opposition figure assassinated Thursday and another political leader killed earlier this year were killed by bullets from the same gun.
Waves of anti-government protesters took to the streets of the capital and other cities Friday, while supporters of the ruling party staged counter-protests. The country's main trade union called a general strike, and flights in and out of Tunisia were grounded.
Many protesters on the streets of Tunis and other cities accused the ruling Ennahda party of involvement in the killing, a claim the party has strenuously denied. That has not convinced Brahmi's widow, Mbarka.
She said the violence happening in Tunisia is not a "simple street fight" between two parties, but "a premeditated violence brought about by the government."
Authorities say Mohamed Brahmi was killed by bullets from the same gun used to murder another opposition politician, Chokri Belaid, in February.
Interior Minister Lotfi Ben Jeddou contends a radical Islamist group of Salafists carried out the killings. Jeddou said the leading figure in the murder plot is Boubacar Hakim, an extremist Salafist and suspected arms smuggler.
Chokri Belaid's murder in February prompted the biggest protests since President Zine El Abidine Ben Ali was swept from power in 2011.
Tunisia's opposition feels Ennahda is doing little to tackle Islamic extremism, said Fatima El-Issawi of the London School of Economics.
"Their way of reacting to this growing intimidation by these radical Islamist voices is conceived to be very weak," he said.
Two Ennahda offices were set on fire Thursday night.
Demonstrators waved Egyptian flags as a sign of solidarity with the protests that prompted Egypt's military to oust Muslim Brotherhood President Mohammed Morsi earlier this month.
Protesters in Tunis say they want the same result. One said "the Egyptian solution" is a possible outcome for Tunisia, too.
But London-based analyst El-Issawi said military intervention would be a major setback for Tunisia.
"Secular Tunisians fell very empowered by what happened in Egypt," she said. "There is a growing movement of rebellion - [like Egypt's] Tamarod - in Tunisia. They are out in the street calling for the toppling of the Ennahda regime. But we don't know what they want. We don't know how they want to implement this change. There are no direct calls for the military to take control of the situation."
Tunisia's Ennahda party has lost an important Islamist ally in Egypt, she said.
"They are definitely very weakened. They are very nervous. They are fearing to see the same scenario, the same Egyptian scenario repeated in Tunisia," El-Issawi said.
The violence comes as Tunisia's lawmakers are finalizing work on a new constitution, due to be put to a public vote in the coming weeks, before presidential elections later in the year.