Mexico City, Mexico - A huddle of tents is conspicuously positioned in front of the federal attorney general's offices in Mexico City.

The encampment, adorned with signs that declare "justice for Bety Carino and Jyri Jaakkola" and "Hunger strike: Day 11", marks as a visual anomaly in the trendy district of Zona Rosa.

Inside, six people on hunger strike are physically sustained by a meagre diet of water and honey. Emotionally, they are buoyed by a small army of local supporters who share their optimism of finally securing justice for their loved ones.

Human rights campaigners Alberta "Bety" Carino and Jyri Jaakkola were murdered on April 27, 2010 in the impoverished mountains of Oaxaca State. They were trying to deliver desperately needed supplies to a rural indigenous community blockaded by a paramilitary gang with alleged links to local government.

Even though arrest warrants were issued in 2012, eleven out of 12 suspected perpetrators from the armed group UBISORT (Union for the Social Wellbeing of the Triqui Region) remain at large. Only the leader of UBISORT is in custody - and he was arrested under other charges. Four years on, the victims' friends and families believe the hunger strikes are their last chance to secure justice.

'We are ready to die'

Omar Esparza, Carino's husband and father of her two children, stopped eating on April 28, a day after the fourth anniversary of the murders.

We will stay here until we are confident that the government will take the proper steps to get justice for Bety and Jyri. - Omar Esparza, Carino's husband and hunger striker

"We are ready to die here, in front of the prosecutor’s offices, because it’s the only option we have left," Esparaza told Al Jazeera on day 11 of the hunger strike.

"We will stay here until we are confident that the government will take the proper steps to get justice for Bety and Jyri; we're tired of empty promises. We are demanding nothing more than that the state fulfil its obligations to us, the Mexican people, and do its job."

In April 2010, Carino and Finnish national Jaakkola were part of a human rights convoy making their way to San Juan Copala, a small town situated in the indigenous Triqui region of Oaxaca, which had been virtually cut off from the outside world for several months by UBISORT.

The Trique is one of the smallest and most marginalised ethnic groups in Mexico.

In 2007, San Juan Copala declared itself an autonomous municipality, rejecting the authority of Oaxaca in favour of governing itself through "traditional indigenous practices".

For decades, local (municipal and state) politicians from the Revolutionary Institutional Party (PRI), which governed the state for 80 years, exploited divisions within the Triques. Politicians selectively financed projects for some clans while ignoring others, to prevent unified revolts, according to Benjamin Smith, an assistant professor of Latin America history and Oaxaca specialist from Warwick University.

The murders

UBISORT was founded in 1994 with financial support from the local PRI, after the Zapatista uprising in the neighbouring state of Chiapas in 1994. Its members are drawn from Trique clans historically rival to San Juan Copala, as well as Mixtecs, which receive state money to fund social programmes. It was classified by the United Nations High Commissioner on Refugees as a paramilitary organisation.

Carino, 35, director of local NGO Cactus (Centre of Community Support Working Together) and Jaakkola, 33 were shot in the head when the convoy was ambushed by 30 armed members of UBISORT; several others were wounded. The region reverted to state control soon after, and many locals fled as a result of the violence.

Rupert Knox, Amnesty International's Mexico researcher, told Al Jazeera: "Jyri and Bety's human rights work supporting those abandoned by the state appears to have been seen as a threat to the armed group. The group enjoyed links with and support of local political representatives and the state government."

Carino, whose zeal for human rights was sparked by Christian social programmes in her youth, left behind two children now aged nine and 12, who were forced to relocate to another state as a result of threats targeting the family.

"Their life changed radically on that day, they lost their mum but in part they lost their dad too. They worry about me, worry about the hunger strike, but they are conscious of the struggle we are in, they understand it," he told Al Jazeera.

By day 13, there is still no response from the authorities. Energy levels are fading, and some of the hunger strikers spend hours lying down in their tents.

'We must fight for justice'

Mexico is one of the most dangerous countries in the world for human rights defenders - particularly for journalists, environmentalists, and activists, according to the United Nations High Commissioner for Human Rights (UN-DH).

The routine failure to hold perpetrators to account leaves many human rights defenders at constant risk of attack - Rupert Knox, Amnesty International

An investigation by the Oaxaca-based NGO EDUCA in 2012, recorded 120 violent attacks against human rights defenders in Oaxaca over 11 months, placing it in the top three most dangerous states.

In 2012, a state judge issued 13 arrest warrants after international pressure from human rights groups, Jaakkola's family, the European Union and Finnish government.

State authorities have said it is too risky to send officers into the communities to make arrests. The state attorney general responsible for the investigation did not respond to Al Jazeera's questions despite repeated requests. Neither did the federal attorney general's office.

Knox said: "The impunity for these crimes is almost total despite daily reports of threats and attacks in different regions of Mexico. The routine failure to hold perpetrators to account leaves many human rights defenders at constant risk of attack."

Jorge Albino Ortiz, another hunger striker and former spokesman San Juan Copala, said: "Bety and Jyri gave their lives for us, defending our human rights even though they were not Triques. We survived, we are alive, and so we must fight for justice. For four years we've knocked on every door looking for justice, nationally and internationally, with no response."

On day 14, a cold front brings driving rain to Mexico City, but the weary six are lifted by news of a high-level meeting scheduled to take place the following day.

A breakthrough

As a response to international pressure then President Felipe Calderon introduced the Protection of Human Rights Defenders and Journalists law in June 2012.

We know there is no guarantee, but we believe this is an important advance. For the first time, we have a promise in writing that state and federal prosecutors will collaborate. - Omar Esparza, Carino's husband and hunger striker

The celebrated law introduced an obligation for state and federal government to provide protection and install prevention mechanisms for those under threat.

While some progress has been made, critics have complained of long delays in assessing cases, inadequately trained staff and a failure to release a $14m ring-fenced budget to fund security measures for those under threat. Only 37 of the 131 applications for protection measures received between December 2012 and February 2014 had been revised by the Governing Board.

At a state level, several noteworthy new institutions have been created in Oaxaca, including Coordination for the Attention of Human Rights in the State Executive and a specialist prosecutor's office to investigate crimes of social significance.

Miguel Angel Vasquez de la Rosa, from EDUCA, told Al Jazeera: "The situation is paradoxical as the new institutions and laws have failed to eradicate the abuses and grievances suffered by defenders. The case of Jyri and Betty shows how ineffective the institutions still are."

According to Professor Smith, "impunity is politically motivated. To arrest the pistoleros [gun men] would risk political links being exposed. So despite the brave, desperate efforts of the hunger strikers I doubt very much the government will lift a finger to do anything about it."

But on day 17, the exhausted hunger strikers in Mexico City report a breakthrough. They, along with the Finnish ambassador, have been assured that state and federal authorities will now work together to investigate the murders. They've been promised justice; the hunger strike is over.

Esparza told Al Jazeera: "We know there is no guarantee, but we believe this is an important advance. For the first time, we have a promise in writing that state and federal prosecutors will collaborate. We will give them this chance, but will monitor progress very closely. If the authorities again fail Bety and Jyri, our only option is seek justice internationally, and we will take the case to the Inter American Court of Human Rights."