The Wrong Address: How a Fatal Arson Opened the Door to a New Era of Digital Police Surveillance

It was just after 2:30 a.m. on August 5, 2020, when Amadou Sow jolted awake to the piercing shriek of his home’s smoke alarms. Flames were already spreading through his house in the Denver, Colorado, suburbs. The 46-year-old rushed to his bedroom door, but a wall of thick smoke and searing heat pushed him back. Panicked, he ran to the rear window, ripped through the screen with his bare hand, and jumped. The two-story fall fractured his left foot.

Sow’s wife Hawa Ka woke their 10-year-old daughter Adama, who shared the couple’s room. She dragged the terrified child to the window and pushed her out. Sow tried to catch her, but missed. By some miracle, the girl landed on her hands and feet and walked away unhurt. Next it was Ka’s turn to jump. She landed on her back, shattering her spine in two places. Sow could barely hear her cries of pain—his mind was fixed on their 22-year-old son, Oumar, who slept down the hall.

He could see no movement through the smoke behind Oumar’s bedroom door. He hurled a rock at the window, but the glass held. Despair washed over him, until he noticed Oumar’s car was missing from the driveway. He must be working his night shift at 7-Eleven. Thank God. Sow’s immediate family was safe, but nine people called the Truckee Street house home. What of the others?

Sow had bought the four-bedroom home in Green Valley Ranch, a newly built northeast Denver suburb, in 2018. Cut off from the rest of the city by miles of open prairie, the neighborhood felt sparsely populated and almost ghostly in its quiet isolation. But for Sow, a Senegalese immigrant who worked overnight shifts at Walmart, it was a sanctuary. Not long after he moved his family in, his old friend Djibril “Djiby” Diol brought his own family to join him. Diol, 29, was a 6-foot-8 civil engineer who dreamed of one day bringing his professional skills back to his home country of Senegal.

The first fire engine arrived on scene at 2:47 a.m. By that time, the inferno had burst through the home’s windows, sending thick plumes of smoke into the sky and filling the neighborhood with the acrid stench of burning wood. When firefighters finally suppressed the blaze enough to enter, they first found the tiny body of Djiby’s daughter Khadija, just two months shy of her second birthday. Further inside, they found Djiby and his 23-year-old wife Adja.

Next to Adja lay Djiby’s 25-year-old sister Hassan, who had only moved into the house three months prior. Like Adja, she had dreamed of returning to school to study nursing. She died with her arms still wrapped around her 7-month-old daughter, Hawa Beye. Medical examiners later concluded all five victims died of smoke inhalation: their airways were caked in black soot, and their internal organs and muscle tissue turned a distinct “cherry red” from exposure to extreme heat.

As firefighters entered 5312 Truckee Street, Neil Baker, a homicide detective with the Denver Police Department (DPD), was woken by a call from his sergeant. Baker, in his fifties with thinning gray hair, reading glasses, and a rosy complexion, threw on a suit, said a hurried goodbye to his wife, and headed for his car.

With nearly 30 years on the job in Denver, Baker knew the city well. He also knew Green Valley Ranch was a confusing maze of nearly identical streets. So before he left, he did what anyone would do: he Googled the address. Like anyone searching for a location, he was focused on getting the directions he needed, not the invisible data packets traveling between his device and Google’s servers, or the automatic logs that record what he searched and where he searched from. But that hidden digital infrastructure would become the key to solving the case—and could soon expand law enforcement’s reach into the private online lives of millions of Americans.

Three weeks before the fire, 16-year-old Kevin Bui drove into central Denver to buy a gun. Bui’s life had shifted from hardship to comfort by the time he reached high school: his family emigrated from Vietnam before he was born, and while they started out poor—Bui describes his childhood homes as “the projects”—his father’s accounting business had taken off by his teen years. The family moved into a sprawling home in Lakewood, on Denver’s western edge, with unobstructed views of the Rocky Mountains. Bui wore Gucci belts and Air Jordans, excelled in school despite disliking classes, and was a standout athlete: a swimmer and an inside linebacker for his school’s football team, the Green Mountain Rams. He was close with his older sister Tanya, seven years his senior; she helped him style his girlfriend’s eyelashes, ranted to him about her own relationship troubles, and the two even talked about adopting a dog together.

But the siblings had a secret side: they sold fentanyl and marijuana, mostly finding customers through Snapchat. Kevin also planned to start “carding” — stealing people’s credit card information from the dark web — and had begun collecting weapons. The men Bui met to buy a gun that July day never followed through on the deal: they robbed him of his cash, his iPhone, even his shoes, before letting him leave.

The robbery left Bui seething with humiliation. By that point in the COVID-19 pandemic, football practice had shut down, and classes had been virtual for months. He felt he was just “doing bullshit”: waking up, logging into Zoom, then going back to bed. The robbery pushed him over the edge. That night back at his Lakewood home, he swore he would get revenge. He pulled up Apple’s Find My Device feature on his iPad to track his stolen phone. The pinging location led him east, past downtown Denver, before stopping in Green Valley Ranch. A pin dropped directly on 5312 Truckee Street.

The next afternoon, Bui sent a Snapchat message to his friend Gavin Seymour, according to later court records: “I deserved that shit cuz I knew it would happen and still went. They goin get theirs like I got mine.”

Bui and Seymour ran track together and lived just a four-minute drive apart, but they were opposites in almost every way. Where Bui oozed confidence, Seymour struggled with crippling insecurity. Where Bui excelled academically, Seymour fought multiple learning disabilities that made school a constant challenge. And unlike Bui’s stable, intact family, Seymour’s parents split when he was young, and his father was largely absent from his life.

Seymour wrote back: “idk why I would let you go alone I’m sorry for that.”

Bui responded: “I cant even be mad cuz we used to do the same shit to random niggas.”

But he was mad. More than that, he was disgraced — his self-image as a winner, a top dog, had been shattered. Over the next week, Bui searched the Truckee Street address 13 times, even pulling up the home’s interior layout on real estate sites like Zillow. He persuaded Seymour, who was just days away from turning 16, and 14-year-old Dillon Siebert, another friend, to help him exact revenge. By late July, Seymour and Siebert had also searched the address multiple times on their own devices.

Bui would later insist they only planned to vandalize the house: hurl rocks at windows, maybe egg the exterior. But in the final sweltering days of July, the plan took a darker turn. On August 1, Bui messaged Seymour: “#possiblyruinourfuturesandburnhishousedown.”

Three evenings later, Siebert and Bui bought black theater masks from Party City, then grabbed dinner at Wendy’s before meeting up with Seymour. Around 1 a.m. on August 5, the three piled into Bui’s Toyota Camry, stopped at a gas station to fill a red fuel canister to the brim, then drove the 30-plus minutes to Green Valley Ranch, passing downtown, the Broncos stadium, and an industrial area dotted with smokestacks and parked semi-trailers. None of the teens spoke up to back out, even when they pulled up to 5312 Truckee and saw a family minivan parked in the driveway.

They found the back door unlocked. It has never been confirmed who spread gasoline across the living room walls and floors, or who lit the match. Once the fire caught, all three stumbled back to the car and sped away.

When Detective Baker arrived at 5312 Truckee Street two hours later, neighbors crowded the street, their faces lit orange by the glow of the still-burning house. The air tasted like ash. He met up with his partner Ernest Sandoval, who had transferred to homicide from the nonfatal shootings unit just weeks earlier and was 15 years younger than Baker. First responders told the pair they expected up to five fatalities, and they initially suspected faulty wiring had sparked the blaze. It was a terrible tragedy, but it seemed like homicide would only be responsible for routine paperwork. “We’ll have some reports to write,” Baker remembered thinking. “We’ll have to probably go to the autopsies.” Then next-door neighbor Noe Reza Jr., a man with melancholy eyes and a faint soul patch, approached them. “I have something you should see,” he said. He pulled out his phone and pulled up footage from his home security cameras.

The clips start at 2:26 a.m., showing three figures in hoodies and masks slipping through the side yard of 5312 Truckee. One gestures toward the back of the house, then they move out of the camera’s frame. Twelve minutes later, the trio sprint back toward the street. At 2:40 a.m., flames burst through the home’s lower floor. Within two minutes, the entire house was engulfed. “Oh, are you kidding me,” Baker thought. Five people had been murdered, and their only lead was a few seconds of grainy footage that revealed nothing about the killers’ identities.

That morning, Bui slept in. Around 10 a.m., he searched online for news of the fire, and found the story dominating headlines across the world. The Council on American Islamic Relations issued a statement urging police to consider religious hate as a potential motive. Leaders of Colorado’s African community voiced fear that other immigrant families could be targeted next. Even Senegal’s president tweeted he would be watching the case closely. That’s when Bui realized he had made a catastrophic mistake.

Like many people, he had assumed Apple’s Find My Device software delivers exact location tracking. But location services rely on an unreliable mix of GPS satellite signals, cell tower pings, Wi-Fi network data, and input from nearby connected devices, and their accuracy can range from a few feet to hundreds of miles. This ambiguity has led to threats, robberies, and even wrong-address SWAT raids in the past. This time, it had led Bui to the home of an entirely innocent family. He had killed five people who had nothing to do with robbing him.

That August, wildfire smoke choked Denver’s normally clear skies, but Baker and Sandoval barely noticed. They spent every waking hour at DPD’s 1970s-era headquarters, under fluorescent lights, working the case nonstop. They started with standard investigative steps: interviewing the victims’ friends and family, combing through text messages and financial records. The more they dug, the clearer it became that the two families at 5312 Truckee led quiet, pious lives centered on work, mosque, and home.

The detectives returned to security camera footage. Clips pieced together from nearby Ring doorbells showed the suspects’ dark four-door sedan making multiple wrong turns entering the neighborhood, and swerving wildly over curbs when they left, but the footage was too blurry to identify the car’s exact make or model. The detectives quickly obtained tower dump warrants, requiring major cell carriers to turn over numbers of every cellular device near 5312 Truckee around the time of the arson. They also obtained a series of geofence warrants requesting Google identify all devices within a defined area just before the fire (at the time, Google collected and stored location data for anyone with an Android device or any Google apps on their phone).

The warrants returned thousands of phone numbers, which investigators passed to Mark Sonnendecker, an ATF agent specializing in digital forensics. A slim, soft-spoken man who bore a resemblance to science educator Bill Nye, Sonnendecker focused first on T-Mobile subscribers, after noticing a “high percentage” of suspects in past cases used the network.

There were 1,471 T-Mobile-registered devices within a mile of the house when it ignited. Using software that maps location based on how long it takes a signal to bounce from a cell tower to a phone and back, Sonnendecker narrowed the list to the 100 devices closest to the home. Toward the end of August, detectives walked the area around 5312 Truckee with a cell tower simulator that captured all device IDs in range that night, getting 723 results. Sonnendecker cross-referenced the two lists, eliminating 67 devices that appeared on both — those belonged to local residents who could be ruled out as suspects. That left 33 T-Mobile subscribers who had no obvious reason to be in Green Valley Ranch in the early hours of August 5.

Investigators considered bringing all 33 in for questioning, but decided against it; without evidence to detain them, they feared spooking the arsonists into fleeing the country. No obvious suspects jumped out, but Sonnendecker remained confident a break would come.

As summer turned to fall, though, progress on the case stalled. Hundreds of Crime Stoppers tips poured in, including several from psychics. Baker and Sandoval traveled across the state and even to Iowa chasing leads that always fizzled out. “We got pretty hopeful here and there, but it just kind of fizzled out,” Baker recalls.

Pressure mounted on the department. After that summer’s nationwide Black Lives Matter protests, a petition demanding police stop “undervaluing the lives of BIPOC individuals” and prioritize the Diol family investigation collected nearly 25,000 signatures. Baker and Sandoval were ordered to drop all other cases and work this one full time.

At a department meeting in September, the pair asked colleagues for any new ideas — was there anything they hadn’t tried? That’s when another detective wondered if the perpetrators had Googled the address before traveling there, and if Google kept a log of those searches. It was like a hidden door they’d never noticed swinging open. They called Sonnendecker and senior deputy district attorney Cathee Hansen. None of them had heard of Google turning over a list of all users who searched a specific term before. While reverse keyword warrants had been used in a handful of prior cases across the country, most of those records were sealed, so the team drafted their own warrant from scratch, requesting names, birth dates, and physical addresses for all users who searched any variation of 5312 Truckee Street in the 15 days before the fire.

Google initially denied the request. According to court documents, Google uses a staged process for responding to reverse keyword warrants to protect user privacy: first it provides an anonymized list of matching searches, and only turns over identifying information like IP addresses after law enforcement confirms which results are relevant. DPD’s first warrant asked for protected identifying information up front, which went too far. It took a second failed warrant 20 days later, and two calls with Google’s outside legal counsel, before the detectives settled on wording the search giant would accept.

Finally, the day before Thanksgiving 2020, Sonnendecker received a list of 61 devices and associated IP addresses that had searched for the house in the weeks before the fire. Five of those IP addresses were in Colorado, and three of them had searched for the Truckee Street house multiple times, including for details of its interior layout. “It was like the heavens opened up,” says Baker.

In early December 2020, DPD served another warrant to Google for the five users’ subscriber information, including their names and email addresses. One turned out to be a relative of the Diols; another belonged to a delivery service. But one name popped out that matched the 33 T-Mobile subscribers they’d flagged earlier as suspicious: Bui.

The phone was registered to Kevin’s sister Tanya — he had likely borrowed it after his own was stolen. A quick check of the remaining subscribers’ social media confirmed three suspects: Kevin Bui, Gavin Seymour, and Dillon Siebert. They were teens, they were friends, they lived 20 miles away in Lakewood, nowhere near Green Valley Ranch. There was no innocent reason for them to be searching a random residential address across the city. “There was a lot of high-fiving,” recalls Sandoval. But it was too soon to celebrate: they had to build a case strong enough to prosecute minors for a high-profile mass homicide. “We knew this was going to be a big, big, big fight,” Baker says.

On New Year’s Day 2021, Baker drove past the Bui family home and snapped a photo of the 2019 Toyota Camry sitting in the driveway. Another warrant to Google yielded the three teens’ full search histories dating back to early July. In the days before the fire, Siebert searched for Party City, and investigators found listings for the same style of black masks the suspects wore on the retailer’s website. Party City confirmed their Lakewood location had sold three of those masks just hours before the fire. Security footage from the shopping center confirmed a 2019 Toyota Camry matching Bui’s was in the parking lot around 6 p.m. that night. “It just snowballed,” says Baker, shaking his head in remembered wonder. “I cannot believe the amount of evidence that we were able to come up with.”

From the teens’ texts and social media, detectives learned that the morning after the arson, while the house on Truckee Street was still smoldering, Bui and Seymour went on a planned camping trip. A week later, Bui played golf. A few months after that, Seymour joined the Bui family on vacation in Cancun, posting smiling photos from the beach and boats. The posts enraged the detectives. “Where’s the remorse?” Baker said.

Shortly after 7 a.m. on January 27, 2021, police arrested Bui, Seymour, and Siebert. Seymour and Siebert refused to talk, but Bui agreed to an interview and promptly confessed. “He’d had six months of just keeping this inside,” said Baker. “He knew that his time had come.”

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