LAS COLINAS, El Salvador (AP) — The schoolboys went missing on a Thursday, and it took nearly three weeks for police to discover the mass grave.

On July 11, a police investigator, wearing a ski mask to hide his identity, dug up the dead, the youngest 15. One of the mothers stood weeping as the corpses were pulled out, along with curious traces of food and silverware.

Gen. David Munguia Payes, El Salvador's minister of justice and security, said the killings were the work of the Mara Salvatrucha, or MS-13, one of two notorious Salvadoran gangs that regularly visited schoolyards to recruit kids — often by force. The police investigator pointed at the buried remnants of a meal. The MS-13 recruiter, he said, had probably tried to persuade the youths to join the group using the usual method: a big meal with cake and soft drinks.

When they resisted, he said, they were stabbed to death.

Six months after El Salvador brokered an historic truce between two rival gangs to curb the nation's daunting homicide rate, officials are split over whether the truce actually works. In March, MS-13 and its rival, Barrio 18, vowed to end the killings and the forced recruitments in exchange for better conditions for incarcerated gang leaders, who run their operations from behind bars. The government transferred 30 bosses of each gang from the maximum security Zacatecoluca prison, nicknamed "Zacatraz," to ordinary jails, where they would impart orders to their minions on the street, purportedly to stick with the truce.

The gangs, which also operate in Guatemala and Honduras, are seeking truce talks in those countries as well.

But Carlos Ponce, an expert on crime for the Salvadoran Attorney General's Office, says the truce is a sham.

"It's all a lie, the gangs continue to operate, people continue getting killed, people keep disappearing and the gangs get stronger and stronger," he said.

The Security and Justice Ministry reports that murders in the first eight months of 2012 are already down more than 30 percent, to 1,894. For the most part, the national medical examiner's office confirms those numbers, but the two agencies disagree on how many people are disappearing. The security ministry says 335 disappeared in the first half of the year; the legal medicine institute says the number is 1,279.

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"These figures are very strange," Ponce said. "They say the murders are going down, they deny the disappearances, but the case of these five students is evidence that everything is still going on. It is very likely that the gangs are adopting new ways to operate." Instead of leaving their victims in plain sight, he said, they are hiding them.

The justice ministry denies that claim, saying its figures are based on investigated disappearances, whereas the medical examiner's office is counting all reports of missing people, many of which are not verified.

"Overall we haven't had an increase. We cannot maintain strict control of the people who are registered as missing because families do not remove their reports when people reappear," Munguia Payes said.

An estimated 50,000 Salvadorans belong to the street gangs that have terrified citizens and left this small Central American nation of 6 million with one of the world's highest murder rates, behind neighboring Honduras. Though meant to stem that violence, the truce does not apply to kidnappings, extortion or drug sales, the core of the criminals' business.

"I think that the truce is a real farce," said Max Manwaring, a professor at the Strategic Studies Institute of the US Army War College in Carlisle, Pennsylvania. "The gangs hold all the cards, and they've been operating out of the jails for years. The jails have become graduate schools for gang members, and the government is simply grasping at straws."

Like others tracking El Salvador's truce experiment, Manwaring doubts the homicide figures.

"There is no way to count them. No way. There are many places government officials simply cannot go to investigate murders because the gangs control the territory."

The truce was mediated by Raul Mijango, a guerrilla in El Salvador's 12-year civil war, then a lawmaker. Speaking to the AP, he said: "Some groups are trying to make the truce look bad, they are killing gang members to create conflicts between the gangs. Saying that the number of disappeared has increased is an argument by those who want to see the truce fail."

Salvadoran security officials have been powerless to contain the violence fueled by gangs, which formed in the jails of California and spread to Central America as their members were deported by the U.S.

In El Salvador, police say, about 10,000 members of Barrio 18 and MS-13 are in jail. The rest are on the streets, and maintain strict control over poor neighborhoods across the country, including inside the nearby town of Las Colinas, where the five boys were found.

In Mejicanos, just outside the capital of San Salvador, Graffiti announces that MS-13 is "the power." Whoever enters must abide by its laws. Rival gangs stay out and police only venture there with elite units and at night.

Once a person enters, gang members come out of their hideouts. Those they recognize are allowed through. Strangers are surrounded, searched, interrogated — then ordered to pay up to move on.

"In order to sell their products, storekeepers must pay a monthly fee. If they do it they survive, but they are always being watched," said Juan Escobar, a soft drink vendor. "If they want their soft drinks you hand them over, or else they get angry."

Neighbors say murders are fewer but fear still rules the streets.

"Yes, it's true that murders have gone down, but we wonder how long the truce will last," said Domitila Martinez, 53, a street vendor in Quezaltepeque, one of the areas with heavier gang activity, some 30 kilometers (20 miles) northeast of San Salvador.

"I can't talk too much, they might kill me, you don't know how they are. We the civilians who find ourselves trapped between the gangs, we have learned to survive."

Under the truce agreement, gang leaders imprisoned with their members can receive "intimate visits" in jail, have plasma TVs in the cells and communicate freely with the outside world.

Joel Nehemias Escalante Quevedo, aka La Rata ("The Rat"), is one of the leaders of Barrio 18 and was interviewed by the AP in the Quezaltepeque jail in San Salvador. He said the idea of the truce arose after 13 people were killed when gang members from MS-13 opened fire on a bus and then torched it.

The violence was getting out of hand, he said, "because our people were running around uncontrolled in the streets."

Reports about the truce in El Salvador led Barrio 18, which operates in both Guatemala and Honduras, to contact its peers in El Salvador with the intention of getting a similar deal.

"What they did in El Salvador is good and we are looking at it like a mirror," said a gang member inside a high-security prison in Tegucigalpa. He asked that his name not be used for fear of reprisals.

Critics of the truce say their interest is not surprising, because it allows the gangs to consolidate their power inside the prisons.

Shortly after agreeing to the truce, the gangs declared schools "peace zones" and vowed to stop recruiting there.

Oscar Luna, Attorney General for Human Rights, said student killings are down. Up until June 22, the National Civil Police reported 41 students murdered, compared to 74 over the same period in 2011.

"Violence still affects society on an alarming level, particularly children, adolescents and young adults," Luna said.

Salvadoran law forbids publishing the names of underage victims of violence, so the boys found in the mass grave were identified by first and middle name only: Kevin Alexis, 15; Jonathan Alexander, 16; Jose Roberto,16; Fernando Alexander, 18; and Jonathan B, 18.

The latter two were brothers and were last seen leaving the Union Centroamericana School in the afternoon in a crowded area of the Santa Tecla neighborhood, on the western outskirts of the capital, officials say.

The multiple stab wounds on their hands and arms suggest they tried to defend themselves, said Jose Miguel Fortin, director of the Institute of Legal Medicine.

The autopsy also determined that the victims had suffered blows to their necks, heads and bodies, the official said.

"I never thought my son would end up this way," wept a mother, as she sat next to the mass grave on a low hill. "I had big plans for my son, he was going to study and have a better life. I never had problems, he was a good kid."

She refused to give her name for fear of reprisals from the gang.

"I don't understand these people," she said. "They are savages."

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Associated Press writers Romina Ruiz-Goiriena in Guatemala City and Alberto Arce in Tegucigalpa contributed to this report.