One evening in September 2014, Mariana Yanez left her home in this crime-plagued Mexico City suburb saying she was going to make some photocopies. Then she vanished.

Months later, authorities called her mother to say her 18-year-old daughter's head and thighs had been found in a sack in a sewage-choked canal, but provided no other details.

Yanez's disappearance is a story shared by all too many in Mexico and nowhere more so than Ecatepec, where Pope Francis is to hold the largest public event of his visit to Mexico when he celebrates Mass on an outdoor esplanade here on Sunday just miles (kilometers) from that canal.

"It's not just one daughter," said Guadalupe Reyes, Yanez's mother. "It's thousands."

Francis has already denounced corruption, violence and drug-trafficking in Mexico ahead of his Feb. 12-17 visit, and he is expected to address those same themes when he delivers his homily in Ecatepec, a sprawling, dangerous, disastrously mismanaged suburb of 1.6 million people.

The pontiff's decision to stop here shines an uncomfortable spotlight on the government's failure to solve entrenched social ills that plague many parts of Mexico — inequality, rampant gangland killings, extortion, disappearances of women, crooked cops and failed city services — even as President Enrique Pena Nieto has sought to make economic reform, modernization and bolstering the middle class hallmarks of his administration. One of Mexico's most shocking crimes in recent years was the 2014 mass disappearance of 43 students in the southern state of Guerrero.

"His Holiness will be in the country's violent, poor and miserable places," and government officials will not be able to gloss over those ills, said a recent editorial in Desde la Fe, a weekly publication by the Archdiocese of Mexico. "The trash remains below the red carpet, and Francis is not coming for the tidy and whitewashed trumpery of the event, nor the colorful confetti."

Known for his work ministering to slums as a cleric in his native Buenos Aires, the Argentine-born pontiff is no stranger to places like Ecatepec.

It's the most heavily populated municipality in the country and part of Mexico state, where Pena Nieto was governor from 2005 to 2011 before leaving office to run for president. However, Ecatepec is usually all but forgotten except at election time, when political bosses arrive with handouts to try to mobilize voters.

Decades of unplanned and unrestrained development have fashioned the city into a carpet of gray slums that climb the surrounding hillsides, intertwined with some better-off areas and industrial zones that, along with the rest of the state, generate almost 10 percent of the country's GDP.

Its location on the northern edge of the capital also makes it a strategic point for drug cartels. Researcher Victor Manuel Sanchez says as many as five were in operation here in 2014. Crime thrives in the shadow of the cartels, feeding off impoverished, unemployed youths and a police force so corrupt that last year the government temporarily barred officers from enforcing traffic laws to keep them from shaking down motorists for bribes.

Homicides rose 9 percent in Mexico last year, and some corners where the cartels are firmly in control suffer the kind of sky-high murder rates seen in neighboring El Salvador and Honduras. Meanwhile, Mexico is also among the most corrupt countries in the world, according to Transparency International, and the second-least likely to punish crimes, according to the University of the Americas in Puebla.

At least 1,554 women have disappeared in Mexico state since 2005, according to the National Observatory on Femicide, and last year the government issued an alert over the killings of women in Ecatepec and 10 other parts of Mexico state.

"Ecatepec is the center of the problem," said Observatory coordinator and lawyer Maria de la Luz Estrada, who is representing the victims in Mariana Yanez's case.

Reyes said she hopes to tell Pope Francis about how she doesn't trust the authorities, who she thinks are in cahoots with the gangs, and about the pain she felt when police said they had found "39 bodies, or body parts," after draining the canal. And about her desperation when state officials then denied those reports, yet didn't even bother to try to determine whose body parts they were.

"They never investigated," Reyes said. "That's why I want to speak with the pope."

A number of victims' groups have requested meetings with Francis, though none have been confirmed. The Mexican Bishops' Council has not ruled it out but says his schedule is very tight.

Francis has met before with those who suffered from organized crime violence, holding a March 2014 prayer vigil in Rome with families of mafia victims. He has called corruption one of humanity's worst sins and speaks pointedly against drug trafficking. In a private letter to an Argentine cleric that provoked controversy last year, he worried about the prospect of "Mexicanization" in his home country and said Mexican bishops told him the drug violence was "terrifying."

On the eve of his trip, Francis said he would pray with Mexicans who confront such challenges. "Because the Mexico of violence, of corruption, of drug-trafficking and cartels is not the Mexico that our mother (the Madonna) wants," he said.

However Papal Nuncio Christophe Pierre has made it clear that the pope, who generally addresses thorny political issues with a diplomat's deft touch, is not coming to Mexico to talk policy or solve the country's problems. Instead, the church has stressed the visit's pastoral nature.

But a simple message of hope may not be enough, said Estrada.

"Hope loses meaning if it is not mentioned in the same breath as truth and justice," she said. "I hope he will bring a strong message of encouragement and faith, but also an appeal for authorities to fulfill their responsibilities and not continue demagoguery and simulation."

While activists hope the visit will draw attention to human rights concerns, authorities are busy beefing up security to avoid any surprises. The government has assigned more than 10,000 police, soldiers and agents of the presidential guard to protect the pope's motorcade and Mass in Ecatepec.

"They told us we could not bring placards or banners," said Guadalupe Fernandez, whose son, Jose Antonio Robledo, disappeared in northern Mexico in 2009, apparently kidnapped by the Zetas drug cartel. "I don't know what we're going to do."

If Fernandez gets one of the 300,000 free tickets being handed out for the papal Mass, it will be her second time seeing Francis. She was there for the vigil in Rome, where she beseeched him to pray for Mexico's disappeared. Francis walked over and clasped her hands.

Now she hopes he will pray for the more than 100,000 people killed and 27,000 missing in gangland violence that exploded after the Mexican government launched an offensive against the cartels in 2006.

Billboards and posters have gone up all over Mexico City welcoming the pope ahead of his visit. Some buildings in Ecatepec have gotten a fresh coat of paint, and worn roads are freshly asphalted. And police have reportedly been quietly removing transients and migrants from Ecatepec's streets for the last month.

But Ecatepec is hard to clean up.

While workers were putting finishing touches on the outdoor stage for the Mass, a dead body was found dumped on the street a few blocks away. Local media said the killers apparently tried to set the corpse on fire.

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Associated Press writer Nicole Winfield in Rome contributed to this report.