GARDNERSVILLE, Liberia — More than 20 years ago, a terrible crime bloodied this suburb of cinderblock homes, dirt-floor stores and lush green bush grass.

Five American nuns were killed when a vicious battle swept through the town during Liberia's civil war. The killers left their bodies burned and broken, rotting in the sun.

The deaths were numerically insignificant in a conflict that by its end in 2003 had left hundreds of thousands of Liberians dead. But the killings crystallized the horror of Liberia's long war for Westerners.

The Catholic Church, the U.S. Embassy and Liberia's Truth and Reconciliation Commission all investigated. All came to a similar conclusion: The killers were soldiers in the army of Charles Taylor, the Liberian warlord convicted by an international court for crimes against humanity.

No killers,  however, have ever been brought to justice. The U.S. Federal Bureau of Investigation eventually launched an investigation. But long delays by the agency and a steadfast reluctance by the Liberian government to prosecute those blamed for atrocities has meant that none of the suspects has ever faced trial, according to an examination by ProPublica and Frontline.

One of those implicated by reports on the killings is Christopher Vambo, a former Taylor commander who used the nom-de-guerre General Mosquito. He is not hard to find. He lives on a rutted street across from a local cemetery in an older part of Monrovia, the country's capital. He works as a security guard for one of the country's largest communications firms.

One hot, rainy day earlier this year, Vambo agreed to an interview — his first with American media outlets since being implicated in the sisters' deaths.

He wanted to speak. But he feared the consequences.

"Christopher Vambo wasn't the one that executed the Catholic nuns, but the Catholic nuns were executed under his command," he said, referring to himself in the third person. "If there is charges for that, there's a penalty for that."

The Sisters

Faith in God and the fury of war defined the lives of the five sisters.

They were members of the Adorers of the Blood of Christ convent based in tiny Ruma, Ill. Most had spent years on mission in Liberia: instructing children, healing the sick, teaching their faith.

Sisters Barbara Ann Muttra, Shirley Kolmer, Kathleen McGuire, Agnes Mueller and Mary Joel Kolmer (a cousin to Shirley) lived, worked and prayed together at a small convent of cinder blocks painted white. It lay just off the main road that runs through Gardnersville, one of Monrovia's outer suburbs.

Muttra, 69, was the best known. A nurse, she had spent 21 years working in Liberia. Her passion was working with mothers and children. She was a bulldog. She faced down soldiers and tendered care at remote clinics.

Shirley Kolmer, 61, was the leader of the group. She was well known among Monrovia's upper middle class. Grinning and gap-toothed, the math teacher served as the first female principal of St. Patrick's High School, an elite all-boy's school in a tony neighborhood of Monrovia. McGuire, 54, the newest arrival, taught there, too. She also supervised a local Catholic grammar school.

Mueller, 62, taught local women to read and worked at a nearby health clinic. Joel Kolmer, 58, taught at the grammar school and mentored young Liberians interested in entering the order.

"These kinds of people must be celebrated," said Kofi Woods, a Liberian human rights leader who knew the sisters.

This account of the lives and deaths of the nuns draws on reports by the Catholic diocese, the Liberian Truth and Reconciliation Commission, and the St. Louis Post Dispatch; a book written shortly after the killings by Sister M. Clare Boehmer called Echoes in our Hearts; confidential transcripts of eyewitness testimony; and interviews with current members of the Adorers of the Blood of Christ, Liberians who knew the sisters, U.S. State Department officials, former Taylor fighters and Vamb o.

Charles Taylor's invasion of Liberia in December 1989 razed the sisters' world. His ill-trained militia and child soldiers slaughtered thousands of Krahn and Mandingo tribal members to settle old grievances.

By July 1990, Taylor's forces were battling Liberian soldiers in Gardnersville. The suburb sat just across from Monrovia, separated from the capital by mangrove swamps and a river. Bullets rained on the convent roof. Artillery crackled.

In August 1990, the sisters decided to flee back to the United States. They would not stay away long, beginning their return in March 1991.

 By then, Liberia had settled into an uneasy ceasefire between Taylor's forces and West African peacekeepers. Taylor controlled much of the country. The peacekeepers protected a caretaker government in the capital.

The ceasefire allowed the sisters to return and rebuild their mission. They scrounged new furniture. They organized residents into Bible groups. They collected Christmas gifts for families receiving treatment at a nearby clinic. More than 30 children had died there since the war's start, victims of severe malnutrition.

Taylor kept busy, too. As detailed in a ProPublica and Frontline investigation, he built up his army in part with the resources of one of America's most iconic businesses: Firestone. The tire giant operated the largest rubber plantation in the world in Liberia. To do business, Firestone agreed to pay taxes to Taylor's rebel army. In exchange, Taylor provided the company protection.

By October 1992, Taylor was ready to launch a massive new assault on Monrovia dubbed Operation Octopus. Using the Firestone plantation as his headquarters, he sent thousands of men streaming toward the capital in the pre-dawn hours of Oct. 15, 1992.

Once again, the rebels struck Gardnersville. They set up mortars and cannons. They fired over the convent into the distant, huddling city.

The West African peacekeeping forces were taken by surprise. They mustered several days before counterattacking. The troops hacked toward Gardnersville, battling through gun-wielding children and rebel strong points.

By mid-October, the sisters were once again on the frontlines of the war.

The Killings

On Oct. 20, heavy combat surrounded the convent.

At about 4 p.m., the convent's security guard grew worried about the violence in Barnersville, a neighboring suburb where his family lived. Muttra and Joel Kolmer agreed to drive him home.

Once the car reached the main road, witnesses saw two West African peacekeepers flag down the car. They got into the vehicle with the sisters. The car headed east on the main road, known today as Somalia Drive. It moved from peacekeeper-held territory toward a checkpoint manned by soldiers from Taylor's army, known as the National Patriotic Front of Liberia, or NPFL.

That's the last time witnesses reported seeing the two nuns, the security guard and the soldiers alive.

When Muttra and Kolmer did not return by nightfall, the remaining three sisters began to worry. By Oct. 23, they had heard nothing. The ineluctable conclusion: Muttra and Kolmer were dead.

By then, the fighting had grown much fiercer. Gunfire rattled constantly. Rocket propelled grenades streaked through the air. Two Lebanese families who lived nearby sought shelter inside the convent.

Surrounded and frightened, sisters Kathleen McGuire, Shirley Kolmer and Agnes Mueller made desperate pleas for help. Informed of their plight, the U.S. embassy asked for assistance from the West African peacekeeping force, known by the acronym ECOMOG.

On the morning of Oct. 23, peacekeepers battled to the convent, but decided evacuation was too risky. The soldiers told the sisters to sit tight. Rescue forces would extract them the following day.

It never happened. That evening, a small squad of Taylor's soldiers approached the convent. They were led by Vambo, according to a church report of the incident based on 10 eyewitness statements. Also present was a young soldier, called C.O. Devil, or Black Devil.

The fighters began shooting AK47s in the air, drawing the sisters outside the convent. Vambo confronted McGuire as she unlocked the gate, shooting her in the arm. She fell to the ground. Vambo executed her by firing into her neck, the report said.

Next, Vambo turned his weapon on one of the Lebanese men, the report said. One shot, and he was dead.

Vambo turned on the remaining sisters and those who had sought shelter. He screamed that he was going to kill all the "white people" in the convent, the report said. He demanded money and keys to the sisters' car.

The two remaining sisters, Shirley Kolmer and Agnes Mueller, lined up against the outside wall of the convent. As they pleaded for their lives, the man named Devil executed the women. Their bodies slumped onto the dirt, leaving trails of blood on the whitewashed wall.

The squad fled with their loot — a car and a pittance of Liberian money.

Taylor's men spared several young Liberian girls, aspirants who were considering joining the convent. They were taken to Taylor territory. They managed to escape and tell their stories to the church and the U.S. embassy. Afterward, several aspirants immigrated to the United States to begin new lives. The order has continued to keep their identities secret.

The aspirants' accounts varied. Some said that Devil had done all the killing. Others blamed both Vambo and Devil.

Their accounts converged on this: Taylor's men had turned the convent into a killing ground.

Mosquito's Attack

In the interview with ProPublica and Frontline, Vambo acknowledged that men under his command may have participated in the attack. But he vigorously denied that he had killed anyone.

Vambo is a small, thin man with a nervous stutter and darting eyes. He wore a cap embossed with the words "Jesus is my Boss."

He sat on the second floor of a shabby restaurant on Monrovia's main boulevard as he told his story, a version of events riddled with inconsistencies.

"I have not talked to lot of people for this," said Vambo, who for years remained a fighter and security advisor for Taylor.

When the 1992 assault on Monrovia launched, Vambo was one of Taylor's most senior field commanders. His mission was to travel from the western side of the Firestone plantation to attack Monrovia's northern suburbs, including Gardnersville and Barnersville. Television footage from the time shows him strolling along Somali Drive, very close to the convent, wearing camouflage, a red beret with a star and aviator glasses. When he speaks, he stutters — then, as now. He shows off the skeletonized remains of West African peacekeepers his men have killed.

Vambo said he was battling for control of the area on Oct. 20 when he got a radio call. Some Caucasians had been killed while approaching a rebel checkpoint in Barnersville. He needed to check it out.

When Vambo arrived, he saw a "military car" burning. Outside lay the bodies of the two sisters, the security guard and the two soldiers. Vambo said he received a full report from the fighters at the checkpoint.

His men told him the killings had been an accident. A vehicle coming from enemy territory approached the roadblock manned by several rebel fighters. One wielded a rocket propelled grenade launcher. When the rebels ordered the pickup to halt, gunfire erupted from the vehicle, Vambo said he was told.

"There's a motto that we got: fire; reply fire," Vambo said. "Our RPG went straight in that pickup, bap!"

Vambo said his men made a mistake: "We were not completely right," he said.

A few days later, on Oct. 23, Vambo said he got another call over the radio. His men told him they had stumbled upon a massacre: three Caucasian women and a Lebanese man, all dead at the nuns' convent.

A unit commander Vambo called Town Devil hailed him on the radio. When Vambo arrived, he saw the bodies lying on the ground. Vambo said he sharply questioned the fighters.

"You people have killed international people and we are not supposed to kill international people," Vambo shouted.

"No, chief, we came here and met the people dead already," Vambo said one man told him.

Approaching West African soldiers frightened the men away. Vambo made a report on the incident to Taylor. The warlord questioned him. Was it possible that his men had committed the massacre? Vambo said he had no proof, one way or the other.

Taylor had Town Devil executed, Vambo said. The other two rebel fighters at the convent were sent to the front lines. Both died in later fighting.

For his part, Vambo heatedly denied having seen the sisters alive. During the interview, he leapt up, gesticulating furiously. He had not killed any of the nuns.

"That's a lie, that's a lie, that's a lie," he shouted. "I never met the Catholic nuns face to face."

"If I did it, God, I will bear the pain for it," he said.

Like many Liberians blamed for atrocities during the war, Vambo exemplifies unfulfilled justice. His accusers have never presented their evidence to a court. Nor has he ever had the chance to clear his name.

"The worst thing I still worrying on is this same Catholic nuns," he said with an anxious look on his face.

"It wasn't I the one that executed the Catholic nuns," he said. "I will continue to say and I will say it over and over."

Taylor assigned John T. Richardson, one of his top advisors, to investigate the incident. Richardson came away uncertain. Taylor's army was such a fluid, ragtag affair that obtaining reliable testimony or reconstructing disputed events was near impossible.

"The way the NPFL fighters move in waves, the wave that's here today isn't there tomorrow.  And nobody will even tell you they remember who was there tomorrow or yesterday," Richardson said. "And so it would have been very difficult to go back in ... and find out what happened on the ground."

The bottom line on whether Taylor fighters killed the nuns? "Could it have happened? Yes," Richardson said.

Outcry

The fate of the women remained a mystery for more than a week, but when the massacre was confirmed, it became an instant symbol of the savagery of Liberia's war.

World leaders decried the nuns' deaths. The U.S. demanded an immediate cease fire. The State Department issued a sternly worded, formal demand, emphasizing that the U.S. would hold Taylor responsible for any crimes committed in his area of control.

Taylor issued cautious denials of responsibility. He said that Senegalese peacekeepers controlled the area at the time the sisters were slaughtered. "It is really no man's land, so it is anybody's guess what has happened to those nuns," Taylor said, according to local news accounts from the time.

Nearly a month after the killings, the fighting calmed enough to allow collection of the sisters' bodies.

At the convent, McGuire's desiccated body was found mostly intact outside the compound. Inside, Mueller and Shirley Kolmer appeared to have been shot, then hacked to pieces with machetes. Their bones were scattered across the compound. With Taylor fighters moving in, West African soldiers collected the two sister's skulls, then scrambled to gather the rest of the bones into a bag for later identification.

At the site of the RPG attack, West African soldiers, Catholic clergy and embassy officials found the incinerated skeletons of Muttra and Joel Kolmer by a burned van. Muttra slumped out of the car, as if she had died inside and fallen out after her door was opened. Kolmer was found partially under the vehicle, as though she had been knocked back by fire.

The nuns' remains were placed into aluminum caskets and loaded into C-130s on the tarmac of Monrovia's municipal airport. They were transported on separate flights back to Illinois, where they were buried in side-by-side graves at the Ruma convent.

Today, a striking, 15-foot high bronze memorial commemorates the sisters' sacrifice. It features the five of them in a circle, hands together, held up to the sky.

A Responsibility Unfulfilled

Gerald Rose was the deputy chief of mission at the U.S. Embassy in Monrovia when the American nuns were killed. He stood on the tarmac as the sisters' bodies were loaded into planes home.

After his retirement from the foreign service, he spent years keeping the sisters' case alive. An Army veteran, he was not about to let America forget that five of its own had been brutally slaughtered. He hectored his congressional representatives. He pleaded with the State Department and the FBI to bring the killers to justice.

Rose's campaign appeared to have an effect. In 2002, nearly a decade after the killings, the FBI opened a formal investigation. Rose was questioned regarding his knowledge of the killings.

At some time in the mid-2000s, Vambo said he was twice interviewed by what he called "CIA investigative reporters." The chief interlocutor in one interview, he said, was named Christopher — the same first name as Christopher Locke, the FBI's lead investigator.

In April 2010, according to a Time magazine account, Locke presented a case to the U.S. Attorney's office in Washington for prosecution. He did not name the suspects. But he told the magazine, "we put together what I personally thought was a prosecutable case."

In 2012, the U.S. Attorney's office decided not to file charges. Prosecutors determined that the statute of limitation had expired on any potential charges against the suspects, a spokesman told ProPublica and Frontline. The agency declined further comment.

The reasons for the decades of delay in investigating the killings are unclear.

Both the FBI and the U.S. Attorney's office declined repeated requests for interviews. The FBI did not respond to a Freedom of Information Act request filed eight months ago seeking records in the closed case of the nuns' deaths. Locke, who has since left the agency, also declined to answer questions.

 "The FBI always continues to diligently work and follow all investigative leads towards the service of justice," the agency said in a written statement.

Indeed, the agency appears to be building a different case against a former Taylor henchman that may include the killing of the sisters.

In May, the agency arrested Tom Woewiyu, Taylor's former Defense Minister. Woewiyu, who has long maintained residence in the United States, was charged with lying on an application for citizenship.

Several months later, the order of nuns contacted the FBI to inquire about the case. Jennifer Lohmeier, an FBI agent, told the order that the agency hoped to file broader human rights charges against Woewiyu that would include the murder of the five sisters.

Cheryl Wittenauer, spokeswoman for the order, also known as the ASC, summarized her conversation with Lohmeier in an email soon after the two spoke by phone this August.

"Apparently, Woewiyu did not give the order to kill the ASC sisters, but he is implicated in that the killings were accomplished under his command," Wittenauer wrote to her supervisors, according to an email obtained by ProPublica and Frontline.

Lohmeier did not return calls for comment. The FBI said they would neither confirm nor deny information regarding Woewiyu's case since it is an open investigation.

However, the press release announcing Woewiyu's capture is headlined: "Alleged War Criminal Arrested." (No known judicial or police authority to date has made such an allegation)

The indictment against him on U.S. immigration violations contains a long history of Woewiyu's role in Liberia's history and civil war. It notes that when Woewiyu was Taylor's minister of defense, Taylor's forces conducted a campaign "characterized by the torture of perceived adversaries, the execution of civilians, the killing of ECOMOG peacekeepers, the forced sexual slavery and rape of girls and women, the conscription of child soldiers, and the murder of humanitarian aid workers" — incongruously strong stuff for an indictment based upon allegations of perjury on Immigration and Naturalization Service Form N-400.

Through his wife, Woewiyu declined comment.

In Liberia, the murder of the sisters became a footnote in a story that grew ever more savage. The war became a hydra, with Taylor's forces one among many rebel groups fighting to control the country.

Taylor was elected president in 1997. The peace that followed was temporary, and the country soon plunged back into a civil war. All told, some 200,000 Liberians were believed killed in the 14 years of conflict. Half of the country's population of 3 million had been displaced.

In the years that followed, Liberia never made peace with its violent past. Charles Taylor was convicted in international court for crimes he committed in neighboring Sierra Leone, not Liberia.

The Liberian Truth and Reconciliation Commission recommended sanctions for scores of people that committed crimes during the conflict — including Vambo. They were never carried out.

The current government has not made punishment a priority. President Ellen Johnson Sirleaf, a Nobel Peace Prize winner elected in 2005, campaigned on a promise to "forgive, not forget."

In an interview with ProPublica and Frontline, Sirleaf said that her government stood ready to charge any individual with war crimes — though the fact is that today, nobody sits in a Liberian prison for the atrocities wreaked upon Liberia and its people.

Sirleaf said that her government had recognized the sisters for "their bravery." She said her critics have overemphasized the importance of punishment in the reconciliation of the country.

"If we were to go fishing for everything that happened before this government, all of our time would be spent doing that and not moving the country forward," Sirleaf said.

For his part, Rose, now 86, said he has not given up on justice someday, somewhere for the sisters.

He describes himself as "unfulfilled and angry."

"I don't think many American people remember that there were five American citizens killed during the Liberian war. Nor do I think many know that the person who killed three of them was identified and that the FBI made a case and presented the case," Rose said.

"I think if the American people were aware of that, they too would feel that justice was not done."

Abel Welwean contributed to this report.

Related coverage: Read more about Liberia's brutal civil war and the American company that played a role in it in Firestone and the Warlord.