Brahmi was the second opposition leader to be assassinated since the ouster of president Zine el-Abidine Ben Ali in January 2011.

The first was Chokri Belaid, who belonged to the same far-left Popular Front coalition as Brahmi, and who was gunned down in a similar fashion on February 6. Authorities say they have arrested suspected accomplices but not the actual killers, and have brought no one to trial.

“Mohamed Brahmi is the second opposition political figure in six months gunned down in the streets,” said Eric Goldstein, deputy Middle East and North Africa director at Human Rights Watch. “The authorities need to actively pursue the killers and make clear that political assassination will not be a part of Tunisia’s democratic transition.”

Brahmi was an outspoken critic of the government, in which the Islamist Ennahdha is the leading party in a coalition with two other parties, Ettakatol and the Congress for the Republic. No one has claimed responsibility for the killing.

Brahmi was a member of the National Constituent Assembly representing the electoral district of Sidi Bouzid, the birthplace of the Tunisian uprising. He was secretary general of the leftist nationalist party The Popular Current until July 7, when he left the party and announced plans to form a new party.

Preliminary information gathered by Human Rights Watch researchers indicates that the assailants shot Brahmi at point-blank range several times at around noon as he was getting into his car in front of his home in the El Ghazala neighborhood of Tunis.

A neighbor, whose house faces Brahmi’s, told Human Rights Watch that she heard a first shot, then several successive shots as if from an automatic gun. She ran out of her house with her husband and son and saw Brahmi sprawled across the car seat, his daughter holding his hand. The neighbor said that another neighbor transported Brahmi to the Mohamed Materi hospital in Ariana, where doctors declared him dead.

Brahmi’s son, Adnen, told Human Rights Watch researchers that he heard a first and a second gunshot, and then several other shots as if from a machine gun. He and his sister ran out of the family’s house and when he arrived at the car, he said, he saw two men riding away on a motorcycle at the very end of the street.

July 25 is Republic Day in Tunisia, a national holiday commemorating the proclamation of an independent republic in 1956.

The killers of Belaid, who led the leftist Democratic Patriotic Party, also shot him at close range several times as he was getting into his car on the morning of February 6 near his home in the Menzah 6 neighborhood of Tunis.

At that time, the Interior Ministry said that the two people who carried out the killing had fled on a motorcycle. The investigations into this assassination have led to the arrest of four people suspected of complicity in the killing, the ministry has said. It said that eight others, including the actual assassins, remain at large.

Tunisia has had repeated incidents of political violence and assaults by people who appear to be motivated by an extremist Islamist agenda, apparently because of the victims’ political or cultural views.

In numerous cases, the authorities appear to have taken insufficient action to investigate and prosecute those responsible, and to prevent further threats to the victims’ lives and security. Human Rights Watch documented several cases in which victims had filed complaints at local police stations or before judges, but never received any indication of follow-up to their cases.

“Tunisia’s pluralistic politics has been an asset to its democratic transition thus far,” Goldstein said. “That transition will go off the rails if assassins can liquidate politicians with impunity.”

Khaled Boujemaa, a human rights activist and an organizer of the festival, told Human Rights Watch that he called the chief of police several times to inform him about threats from people he identified from their beards and clothing as salafists. The officer ordered the organizers to cancel the festival, and accused them of being Shi’a, Muslims who are in the minority in Tunisia. When a large group of bearded men started tearing down the photos and the flags posted for the event, Boujemaa made another call to the police, but the police did not intervene to protect him, or the participants, and they were severely beaten. The police visited the victims in the hospital, and an attempt to identify the assailants was made, but nothing was heard since and nobody knows if a trial will take place or when.

As Joe Stork, deputy Middle East and North Africa director at Human Rights Watch, states: “The failure of Tunisian authorities to investigate these attacks entrenches the religious extremists’ impunity and may embolden them to commit more violence.”

It is clear that the extremis tend to target artists, intellectuals, and political activists. Some of the victims are drama teachers and civil society activists, assaulted on October 14, 2011, and again on May 25, 2012, in Le Kef; organizers for Doustourna, a social network, attacked on April 21, 2012, in Souk Al Ahad; journalists, documentary filmmakers and philosophy professors, intimidated on May 25, 2012, in Bizerte and May 30, 2012, in Tunis.

Based on the victims accounts, these attacks have taken place in the past 10 months in various parts of the country by people having similar clothing and appearance. The attackers used weapons such as swords, clubs, and knives to prevent festivals, gatherings or celebrations, and have beaten people, apparently for their ideas, dress, or activity.

In all cases the victims filed complaints at the police stations immediately after the assault, in most cases identifying the attackers. As far as Human Rights Watch has been able to determine, police have not arrested any of the alleged attackers, or initiated formal investigations or prosecutions against them.

Four men are in custody and we are interrogating them because they are suspected of helping instigate the events at the US consulate,” Wanis Sharif Deputy Interior Minister told the Reuters news agency on Thursday.

Meanwhile, demonstrations against an anti-Islam film made in the US have spread to several countries across the Middle East.

Hundreds of protesters stormed the U.S. Embassy compound in the capital Sanaa, chanting “death to America”  removing the embassy’s sign on the outer wall. Clashes between police and demonstrators near the US embassy in Sanaa on Thursday killed 4 people and wounded another 34, a security official said, according to Al Jazeera.

At the same time, protesters clashed with police near the U.S. Embassy in Cairo for the third day in a row. Police used tear gas to disperse the demonstrators. Sixteen protesters and 13 policemen were wounded in the clashes, which broke out overnight. Twelve protesters have been arrested, the Interior Ministry said. American flags were also burned in Tunisia, outside the US embassy in the capital of Tunisia.

US President Barack Obama has called the leaders of Egypt and Libya to discuss security co-operation following the violence in Cairo and Benghazi, the White House has said. Barack Obama, the US president, has vowed to bring to justice those responsible for the Benghazi attack. Secretary of State Hillary Clinton said Washington had nothing to do with the video.

Innocence of Muslims, the film that mocked Prophet Mohammad, was produced in the US by a filmmaker with ties to Coptic Christian groups, and excerpted on YouTube with dubbing in Arabic.