Of all the dozens of suspected thieves questioned by the detectives of the Train Burglary Task Force at the Los Angeles Police Department during the months they spent investigating the rise in theft from the city’s freight trains, one man stood out. What made Victor Llamas memorable wasn’t his criminality so much as his giddy enthusiasm for trespassing. He was a self-taught expert of the supply chain, a connoisseur of shipping containers. Even in custody, as the detectives interrogated him numerous times, after multiple arrests, in a windowless police-station room in the spring of 2022, a kind of nostalgia would sweep over the man. “He said that was the best feeling he’d ever had, jumping on the train while it was moving,” Joe Chavez, who supervised the task force’s detectives, told me. “It was euphoric for him.”

According to detectives, Llamas divulged how he learned to decode the containers stacked on freight trains through his repeated break-ins and by Googling the placards, locking devices, logos and numbers on the containers, which often provided clues to the loot he might find inside. An upgraded lock was a sure sign of more valuable contents. Inside the containers — most of them were secured with metal locks about the size and shape of a corkscrew that easily succumbed to his bolt cutters or mechanized handsaw — the items were varied and plentiful: TVs, beer, clothing, makeup, shoes, electric bicycles, hard drives, tablets.

Llamas worked with Connie Arizmendi, his girlfriend at the time. After becoming aware of them, the detectives put a tracking device on the couple’s S.U.V. and followed them around Southern California. The couple would set up in a motel near the tracks somewhere out in the inland empire or farther south; they ranged as far as Barstow, more than 100 miles to the east. After nightfall, they would hit the trains and then often shuttle cargo back to their motel rooms for storage. By that point, Chavez, who is 58, had been at the L.A.P.D. for nearly 35 years, working homicides, drugs, gangs, auto thefts and robberies, and he had never heard anyone talk about his crimes as rapturously as Llamas. “He straight out told me, he goes, ‘Detective Chavez, I’m never going to stop doing it,’” Chavez says.

Some 20 million containers move through the ports of Los Angeles and Long Beach every year, including about 35 percent of all the imports into the United States from Asia. Once these steel boxes leave the relative security of a ship at port, they are loaded onto trains and trucks — and then things start disappearing. The Los Angeles basin is the country’s undisputed capital of cargo theft, the region with the most reported incidents of stuff stolen from trains and trucks and those interstitial spaces in the supply chain, like rail yards, warehouses, truck stops and parking lots. Cases of reported cargo theft in the United States have nearly doubled since 2019, according to CargoNet, a theft-focused subsidiary of Verisk, a...