Chanting and waving signs to protest high electricity prices, thousands of unarmed indigenous demonstrators blockaded a highway in western Guatemala, forcing a standoff with police. Two truckloads of soldiers arrived and gunfire erupted, killing eight protesters and wounding 34.

What happened next after the Oct. 4 incident was virtually unprecedented in a country scarred by decades of civil war as well as violence against its indigenous majority and years of impunity for its powerful military. Authorities actually investigated the violence, and the alleged perpetrators were arrested.

The country's attorney general, a former human rights activist known for her bold pursuit of criminals, dispatched at least 175 prosecutors and investigators to the scene, and many of them collected shells, blood samples and DNA evidence. Others travelled to two nearby hospitals to interview wounded demonstrators and witnesses.

Within a week, prosecutors had detained eight army privates and a colonel on criminal charges. Two privates and the colonel could each face a maximum penalty of 500 years in prison for extrajudicial assassination while six privates could face up to 320 years each for attempted murder with intent. An accompanying report said soldiers had ignored police instructions to stay away from the protest.

The soldiers involved were not recipients of any U.S. aid or training in a Central American country in which the United States has spent $85 million fighting drug traffickers since the civil war ended in 1996.

President Otto Perez Molina pushed to end an earlier U.S. ban on military aid that was imposed during the conflict over concerns about human rights abuses. To fight the drug trafficking problem, Perez has since approved the creation of two new military bases and the upgrading of a third to add as many as 2,500 soldiers. He's also signed a treaty allowing a team of 200 U.S. Marines to patrol Guatemala's western coast to catch drug shipments.

Perez, a former army general who's been investigated for human rights abuses during the country's civil war, lent his support to the investigation into the shooting of protesters earlier this month, saying he would accept the attorney general's actions. He also pledged never to use troops again to quell the protests, blockades and land takeovers frequently employed by Guatemala's mostly poor majority to denounce government policy.

Outside observers said the prosecution, after a series of government attempts to exculpate the soldiers, is largely attributable to the political power of Claudia Paz y Paz, 46, an aggressive attorney general who enjoys support from the U.S. and other countries that provide essential aid to Guatemala. That's given her the clout to face down the president and the military and ward off obvious attempt to thwart or quash her prosecution.

Within 24 hours of the shooting outside the town of Totonicapan, Paz had deployed prosecutors from five offices spanning three different states, crime scene specialists and investigators. The overwhelming majority of the teams had received international training funded by the Spanish and Canadian governments, said Jose Arturo Aguilar, the attorney general's secretary of strategic and private affairs.

"The role of the public ministry is to consolidate justice as a fundamental mechanism for strengthening our democracy," Paz told The Associated Press.

A spokesman for Perez said his acceptance of the prosecutor's actions showed his commitment to reforming a country marred by corruption and impunity.

"The president's reaction ratifies his promise of strengthening the rule of law that will fortify Guatemala's democracy," spokesman Francisco Cuevas said.

Guatemala has widespread institutional corruption, "including unlawful killings, drug trafficking, and extortion; and widespread societal violence, including violence against women and numerous killings, many related to drug trafficking," according to a recent State Department report.

Experts said the president's recent actions mark a dramatic shift in a country once known for its reluctance to punish its military. In fact, the prosecutions are the first of troops accused of illegally suppressing protests since the end of Guatemala's civil war in 1996.

"It is an important departure from Guatemala's long history of impunity for similar crimes," said Kelsey Alford-Jones, director of the Washington-based nonprofit group Guatemala Human Rights Commission/USA. "Justice in this case, along with the demilitarization of citizen security, will be a significant step toward ensuring non-violent resolution of social conflict in the future."

Protester representatives called the prosecution a step forward but told local media that they still wanted to see the interior minister and defense minister resign.

Since assuming leadership of the public ministry in 2010, Paz has vigorously pursued military officials and other suspects, putting four civil war-era generals on the stand for crimes against humanity and genocide charges after their cases stalled for decades. She's also pushed for international training of prosecutors to carry out science-based prosecutions.

"We're now seeing the successes of the public ministry. It is an institution that is acting with autonomy," said Marlies Statters, director of Impunity Watch, an international watchdog organization that monitors whether governments comply with legal obligations to crime victims.

The real test for Paz and her prosecutors will be parlaying the arrests into just trials, said Anita Isaacs, a longtime Guatemala scholar and a professor of political science at Haverford College in Pennsylvania. She pointed out that the public ministry belongs to a judicial system still considered highly inefficient and, in many ways, corrupt.

Paz, for one, appears to be taking that charge seriously. Her aggressive prosecutions and reputation for staying above corruption have won her the backing of the U.S. government, which provides millions in aid to Guatemala and has some 200 marines in the country on anti-drug missions. Paz is the only senior Guatemalan official to have met with U.S. Secretary of State Hillary Clinton.

Diplomatic insiders say the U.S. has made no secret of its insistence that Perez keep Paz, support the CICIG and reform the country's weak national justice system.

"Claudia Paz is backed by the international community because of her efficiency and professionalism. That's something President Otto Perez Molina recognizes and respects, too," said Rene Mauricio Valdes, resident coordinator of the United Nations in Guatemala.

Military action against civilians is a highly sensitive topic in a country scarred by a 36-year war between right-wing paramilitary groups and Marxist guerrillas that led to the deaths of some 200,000 people — most of them Mayan Indians. Many were raped, tortured and executed in mass killings.

Meanwhile, conservative voices, mostly from Guatemala's business elite, warned against comparing the protester shooting outside the town of Totonicapan to the civil war.

"We must be calm and be mindful not to use this event to rehash the past," said Andres Castillo, president of the Coordinating Committee of Agricultural, Commercial, Industrial, and Financial Businesses. His office filed an official complaint with the public ministry that the indigenous groups were violating members' right of movement by blockading the highway.

Guatemala has also long been under international pressure to bring those responsible for war crimes to justice. A 2006 treaty-level agreement with the United Nations created the International Commission against Impunity in Guatemala, known by its Spanish acronym CICIG. The independent body has 50 international prosecutors, police officers and attorneys charged with investigating a limited number of sensitive cases.

CICIG has successfully prosecuted several high-profile cases but its longer-term mission is strengthening the attorney general's office and other state institutions before the commission leaves Guatemala, expected after 2015. It's overseen the hiring of hundreds of prosecutors, many assigned to new investigative units, and helped train them to use forensic evidence in trials.

According to a public ministry report, the ballistic evidence shows soldiers opened fire at the protesters, contradicting initial claims by the president and other government ministers that the soldiers were unarmed and later claims that they were armed but fired only into the air.

The president told reporters last week that armed security guards had driven the soldiers to the protest and one of the guards apparently was the first to start shooting. Then an unspecified number of soldiers fired to protect themselves from what they considered a threatening crowd, Perez said. Paz said all soldiers who fired their weapons were arrested.

Ricardo Guzman, deputy undersecretary general for the attorney general's office, said Guatemala's defense ministry cooperated fully with the investigation, providing the roster of every soldier present at the scene. Guzman said all of the soldiers' weapons were surrendered to his office for investigation and investigators had matched the bullet fragments from each body to specific soldiers' weapons.

"What happened at Totonicapan was a terrible tragedy. But with this investigation we watched an independent public ministry at work," said Michael Frulhling, Swedish ambassador to Guatemala. Since CICIG's creation, Sweden has donated over $13 million to the commission.

Alberto Brunori, a representative of the U.N. Office of the High Commissioner for Human Rights in Guatemala, said the public ministry's findings match those of his office. He said such results would have been unthinkable only a few years ago.

"Paz y Paz's investigation proves two things: CICIG's ability to provide technical training and the level of professionalism the public ministry is acquiring," Brunori said.


Romina Ruiz-Goiriena on Twitter: http://twitter.com/romireportsAP