Tunisia is blaming al-Qaida-linked extremists for killing a leading opposition politician.
Interior Minister Loutfi Ben Jeddou said Friday that Mohamed Brahmi of the secular Popular Front party was shot 14 times during a daytime attack.
"The shocking finding is that the 9 mm automatic weapon used in this murder is the same weapon that was used to assassinate martyr Chokri Belaid."
As with the killing of opposition leader Chokri Belaid in February, Brahmi's shooting on Thursday has sparked mass protests and a general strike.
Interior Minister Jeddou says investigators believe the assassin is Boubakr Hakim, a weapons smuggler with jihadi sympathies. Hakim is still on the loose.
Police used tear gas to try to disperse protesters who took to the streets of the capital, Tunis, overnight. But many said they would not be deterred.
"We are all against Ennahda. We are all exposed to bullets now. What if I am shot dead? But now, I am ready to die for the sake of my country."
Many of the protesters are blaming the country's ruling Ennahda party for the assassination, saying the moderate Islamist part had not done enough to cut off funding or support for more extremist groups.
The Popular Front's Brahmi was a vocal critic of Tunisia's Islamist-led government and was helping draw up a new constitution.
His widow, Mbarka Brahmi, on Friday called for Tunisians to revolt.
"Today, Ennahda has been bought by a gang using dirty money brought from suspect foreign sources. Ennahda is using this money to kill the father of my children and leave them orphaned so as to silence the voice of truth. The people must not miss this chance to overthrow the government. This system is dirty and treasonous. The people missed their chance on the day of the funeral of Chokri Belaid and didn't take advantage of the moment. If they this miss this opportunity, the funeral of Mohammed Brahmi, then the people deserve what they get."
Also Friday, Popular Front spokesman Hamma Hammami said the party was ready to launch an alternative government.
"We (the opposition) agreed that this is the end of legitimacy of the National Constituent Assembly and institutions that emanate from it, as the presidency and government are over now."
Ennahda, which rules in a coalition with two secular parties, has condemned the killing.
The chairman of the Constituent Assembly declared Friday a day of mourning.
Thursday's killing comes as Tunisia was celebrating the 56th anniversary of becoming a republic after gaining independence from France.
Tunisia's 2011 uprising ousted autocratic President Zine al-Abidine Ben Ali and sparked a wave of similar protests across the Middle East and North Africa.