Joe McElroy got into his Honda sedan one morning in late 2020, turned the key, and heard a loud screech. Gotdamn, he said. As a mechanic, he knew instantly that his cars catalytic converter a football-sized device on the undercarriage between the engine and muffler that reduces environmentally harmful exhaust emissions had been stolen, sawed off overnight while the car sat in the driveway. Replacing the missing part set him back $900. McElroy, who is 74 and has lived in Sacramento all his life, had never suffered this sort of theft before.

Its an experience that has become more common across the country, especially in California, where property crime has increased since the start of the pandemic, contributing to recall campaigns that ousted the district attorney in San Francisco and aimed to do the same in Los Angeles . While news footage of robberies at convenience stores and smash-and-grabs at luxury boutiques offered recall supporters dramatic evidence of lawlessness in the state, the crime trend that has most directly affected the highest number of residents is catalytic converter theft, an act swift, invisible, and silent until the screech of broken exhaust pipes the following morning.

McElroys block on Meadowgate Drive in Sacramentos southern suburbs felt tranquil and safe, lined with cypress and palm trees that framed bungalows with two-car garages, broad driveways, and lawns yellowed from drought. He often spent his evenings sitting in a plastic chair in his garage with the door open, smoking a cigarette, watching the leaves in the breeze, rarely a pedestrian or passing car in sight.

His next-door neighbors, the Vang family, warmly welcomed him when he moved in five years ago. Brothers Tou and Andrew and their mother, Monica Moua, invited him over for barbecues in their backyard, where McElroy saw the chickens they raised and met the cousins, aunties, and uncles who often dropped by the house. When there were leftovers, Monica brought McElroy and his family heaping plates of Hmong staples boiled meat, spicy vegetables, white rice. After Andrew learned that he and McElroy shared a passion for fishing, hed swing by after daylong sessions on the American River to show photos of the trout and bass hed hooked. Tou often seemed too busy with work to socialize much most of the time I saw him, he was going somewhere, McElroy said but was always friendly and sometimes paused to talk shop with his mechanic neighbor.

Automobiles were an essential component of Tous entrepreneurial ambitions. McElroy recalled Tou talking about starting a trucking business, before eventually creating Vang Auto Core LLC in May 2019. Registration filings described its services as recycling used or unwanted car parts. Andrew worked at the company too.

The family appeared to be living comfortably but not lavishly. They rented their two-story house. Their new vehicles werent luxury brands but Toyotas. They blended into the fabric of the neighborhood, and to McElroy, the thing that stood out most about them in his memory was the kindness they showed him.

Nice family, McElroy said of the Vangs. Very good neighbors. All of em was cool cats.

One afternoon in November 2021, McElroy returned home from work to find police cars all over the block. Yellow crime scene tape encircled the Vangs house. A tarp covered a dead body on the driveway. Asking around, McElroy learned that Andrew had fatally shot a burglar whod broken into the house.

Then, he watched a stream of officers march through the front door with dogs and sledgehammers. From his garage, he could hear the destruction.

Cops come over and fucked up the whole house, he said. Just ransacked it. Knocking the walls down. They destroyed it.

The Vangs moved out a few days after that, swiftly and silently, without any goodbyes. It took the landlord eight months to repair the house and find a new tenant. Even after another family moved in, McElroy still had no idea what happened to his old neighbors.

In fact, Tou, 31, Andrew, 27, and Monica, 51, were arrested in October 2022 and accused of being part of a nationwide theft ring that moved half a billion dollars worth of catalytic converters over three years. Prosecutors brought charges against 21 defendants across five states in what has emerged as the first major federal criminal case seeking to expose the vast scope of the catalytic converter black market and its role in a global supply chain that stretched from California to New Jersey and Japan.

The demand for catalytic converters traces to one of their essential components: palladium, a rare metal that has become one of the most valuable minerals in the world. From early 2016 to early 2019, the per-ounce price of palladium tripled from around $500 to $1,500, exceeding the value of gold for the first time in nearly two decades. Over the next three years, the number of catalytic converter thefts soared in the US: State Farm reported that its insurance claims for that crime rose by 400% from 2019 to 2022; the National Insurance Crime Bureau announced that its data showed a 1,215% increase; law enforcement agencies in San Francisco, Tulsa, and New York City have announced sharp surges, as have police departments in Chiba, in western Japan, and London. A single catalytic converter can contain up to 7 grams of palladium, as well as 7 grams of platinum, whose value has stood for years at around $1,000 per ounce, and 2 grams of rhodium, whose per-ounce price leaped from around $650 in 2016 to $2,500 in 2019.

The palladium boom triggered a catalytic converter rush that car owners, local legislators, and law enforcement agencies are struggling to contain, as rising living costs and stagnant wages continue to drive people into desperate circumstances without clear paths to upward mobility. Hundreds of pages of court documents reviewed by BuzzFeed News reveal that stolen catalytic converters are not simply the beginning of an underground supply chain but a link in a self-sustaining cycle: the palladium inside gets extracted and ultimately sold back to car manufacturers who need it to make more catalytic converters, which are in ever-rising demand because of these thefts.

Through a family representative, the Vangs declined interview requests for this story.

Asked how he felt to learn about the allegations against the neighbors hed grown fond of, McElroy remained steadfast.

I miss em, he said.

A good cutter can slice the catalytic converter off a car in less than one minute. With a partner keeping an eye out for witnesses, the cutter raises the vehicle with a jack, slides into the narrow space beneath, and removes the cylindrical hunk of metal with an electric handsaw.