It started with a missing person report. Just one. Reyna González went to a small house in the Lomas de San Miguel neighborhood of Atizapán de Zaragoza on May 14, 2021, and she never came back out. Her husband, a police commander who wasn't about to let the "red tape" of Mexican bureaucracy slow him down, broke into the house himself. What he found wasn't just his wife’s remains; it was a scene so horrific that it forced the entire country to look into an abyss that had been widening for decades.
Andrés Filomeno Mendoza Celis wasn't some shadowy figure lurking in the woods. He was a 72-year-old neighbor. He gave out food to the poor. He was a former butcher. He was the guy everyone thought was just a "quiet old man." But when the floorboards were ripped up, the Monstruo de Atizapán became the face of the most prolific serial killer in Mexican history.
The Basement Under the Floor
The sheer scale of this case is hard to wrap your head around. Honestly, even the forensic investigators from the Fiscalía General de Justicia del Estado de México (FGJEM) seemed overwhelmed as the days turned into weeks. They didn't just find a body; they found a catalog.
Mendoza had a basement—a cramped, dark room he’d built beneath his house. In that space, investigators found thousands of bone fragments. We aren't talking about a dozen or so. Initial reports cited over 4,000 fragments, but as the excavations continued, that number climbed past 19,000.
Think about that for a second.
Nineteen thousand pieces of human remains under one small house in a crowded suburb. The forensics team had to literally dismantle the structure, digging through the foundation of the kitchen and the bedroom. It wasn't just bones, either. They found women's clothing, handbags, makeup, and—perhaps most chillingly—ID cards belonging to women who had been reported missing years, even decades, earlier.
🔗 Read more: The Faces Leopard Eating Meme: Why People Still Love Watching Regret in Real Time
A Killer’s Ledger
One of the most disturbing pieces of evidence was a series of notebooks. Mendoza was meticulous. He didn't just kill; he recorded. He wrote down names, dates, and descriptions of his victims. He even noted the weights of body parts. It's the kind of detail that makes you realize this wasn't a crime of passion or a momentary break from reality. This was a long-term, calculated operation carried out by someone who felt completely untouchable.
The ledger, along with several 8mm and VHS tapes found in the home, suggested the killings went back to at least 1990. For over thirty years, the Monstruo de Atizapán operated in plain sight.
Why Nobody Noticed for 30 Years
It’s the question that haunts the families: How?
Mexico is currently facing a femicide crisis that is, quite frankly, a national emergency. Statistics from the Executive Secretariat of the National Public Security System often show an average of ten women murdered every single day in the country. In that environment, a missing person often becomes just another file in a cabinet.
Mendoza chose his victims carefully. Many were women he met in bars or around the neighborhood. He would offer them help or invite them over. Because he was an elderly man who was active in local community politics—he was actually a neighborhood council president at one point—no one suspected him. He used his "kindly neighbor" persona as a literal shield.
💡 You might also like: Whos Winning The Election Rn Polls: The January 2026 Reality Check
But there’s also the butcher factor. Mendoza knew anatomy. He knew how to "process" a body efficiently. This is a grim detail, but it’s essential to understanding how he managed to hide so much evidence in such a small space. He wasn't just dumping bodies; he was destroying them. There have even been harrowing reports and testimonies from the trial suggesting he may have consumed or even fed the remains to neighbors under the guise of them being carnitas, though investigators have handled these specific claims with extreme sensitivity to avoid further traumatizing the community.
The Trial and the 4,343 Fragments
The legal proceedings were relatively swift compared to the decades he spent at large. In March 2022, Mendoza was sentenced to life in prison for the murder of Reyna González. But that was just the beginning. The state has been working through the DNA of the thousands of bone fragments to link him to other specific disappearances.
As of late 2023, forensic experts had identified at least 19 distinct victims from the remains found in the Atizapán house, but based on the notebooks and the sheer volume of bones, the actual number is feared to be much higher—potentially over 30.
The case of the Monstruo de Atizapán has forced a massive re-evaluation of how missing persons reports are handled in the State of Mexico. It exposed a massive gap in how "low-risk" individuals (like the elderly) are profiled by law enforcement. It showed that the "monster" doesn't always look like a monster.
What This Means for Justice in Mexico
If you’re looking for a silver lining, there isn't much of one, but the case did lead to the "Ley Monse" and other legislative pushes to crack down on those who help cover up femicides. However, Mendoza mostly acted alone, which makes his story a singular, terrifying outlier in the criminology of the region.
📖 Related: Who Has Trump Pardoned So Far: What Really Happened with the 47th President's List
The house in Atizapán has been largely demolished during the search for remains. What remains is a scar on the neighborhood. For the families of the missing, the discovery was a double-edged sword: the agony of knowing the truth, but the finality of having a place to mourn.
Actionable Insights and Safety Realities
While it’s easy to get lost in the "true crime" aspect of this, there are real-world takeaways regarding community safety and systemic failures.
- The Myth of the Profile: The biggest mistake neighbors and authorities made was assuming a 70-year-old man couldn't be a violent predator. Criminal profiling is moving away from "age-based" assumptions for this very reason.
- The Power of Immediate Search: Reyna González’s body was only found because her family didn't wait. They took the search into their own hands. In Mexico, the first 24 hours are critical, and the "Alerta Amber" and "Protocolo Alba" systems are the primary tools for this.
- Support for the Families: Organizations like Voces de la Ausencia provide actual support for families of femicide victims. If you are following this case to understand the broader context of safety in Mexico, supporting these grassroots forensic and legal advocacy groups is the most direct way to help.
- Digital Footprints: One thing that helped investigators eventually map out his timeline was the recovery of old electronics. In modern disappearances, the "digital trail" is often more reliable than physical evidence in the early stages of an investigation.
The Monstruo de Atizapán isn't just a horror story; it's a testament to the fact that evil often wears a very boring, very ordinary mask. It's a reminder that vigilance isn't about being paranoid—it's about not letting the "ordinary" nature of a person blind you to the red flags of their behavior.
Stay informed by following updates from the Fiscalía del Estado de México for the ongoing DNA identification results, as many families are still waiting for that final, definitive confirmation.