The State Legislature responded with the Street Terrorism Enforcement and Protection Act (STEP Act), Statute 186.22 of the penal code, which, for the first time, legally defined “gang” in the state of California: a formal or informal group of three or more, sharing a common identifying name, symbol or sign, and whose primary activity is crime. The law augments a prison sentence, adding anywhere from two years to life, depending on the severity of the underlying conviction. The Los Angeles County district attorney at the time, Ira Reiner, whose office helped draft the law, said it would help “to rid the streets of hoodlums that are terrorizing and killing our citizens.” Similar laws are now in place in 31 states across the country.

In Modesto, the vast majority of documented gang members are Latino, and most of them affiliate, however loosely, with either Sureños, from Southern California, or Norteños, from the northern part of the state. The line dividing the two groups is imaginary and constantly in flux. Each group has its own symbols (the number 13 for Sureños, 14 for Norteños, both often represented as Roman numerals) and colors (blue for Sureños, red for Norteños) and even their own strain of gangster rap (indistinguishable to the untrained ear, save the different metaphorical targets in the graphically violent lyrics). At the Sebourn trial, Brennan showed the jury and his witness, Robert Gumm, a Modesto Police Department detective, image after image of Sebourn’s extended network of friends, photos of young men and women throwing up signs for the number 13, contorting their fingers into crooked forms of the letters CLS, for Celeste Locos Sureños, Sebourn’s clique from the neighborhood near Celeste Street, on the east side of Modesto. Most of the pictures had been taken from the defendants’ cellphones, as well as from their Facebook pages. The jury saw photos of tattoos, of young men drinking 40-ounce bottles of malt liquor, scowling at the camera. It was a gangbanger’s photo album, or at least that was what this curated selection of images appeared to be. And though Sebourn himself was in only a couple, Brennan argued that he was known to these young people, as they were known to him. It was guilt by association. And it was very convincing. That rainy morning in Modesto, I had two contradictory thoughts at once: This doesn’t seem fair; and These knuckleheads sure look like gang members.

In Stanislaus County, as in many counties in California and across the United States, law-enforcement officers keep a database of individuals that they have identified as gang members. From their point of view, these lists are vital and necessary, but activists argue that they can be discriminatory. Researchers have found that white gang membership tends to be underestimated and undercounted, while the opposite is true for black and Latino youth. In 1997, California created a statewide database, called CalGang, and by 2012, according to documents obtained by the Youth Justice Coalition, there were more than 200,000 individuals named in it (roughly the same number as the population of Modesto), including some as young as 10. Statewide, 66 percent were Latino, and one in 10 of all African-Americans in Los Angeles County between the ages of 20 and 24 were on the list.

When the STEP Act became law, there were dissenting voices, some of them unsurprising, like the American Civil Liberties Union. But there were others you might not expect: Among law-enforcement authorities, for example, there were concerns that the STEP Act could be applied too broadly. Wes McBride, a retired sergeant of the Los Angeles County Sheriff’s Department and the executive director of the California Gang Investigators Association, told me that although he has come to see the law as valuable, he was initially skeptical. “We thought the original writing of that bill was bad,” he said. “It made being a gang member a crime, and that flies in the face of the Constitution, in my mind. What’s to stop the Boy Scouts from being considered a gang?” Shortly after the STEP Act went into effect, The Los Angeles Times quoted an anonymous law-enforcement official expressing concern: “I realize that we have to do something, but when you have carte blanche, it’s difficult not to abuse it.”

A quarter of a century later, this point is still being raised. Manohar Raju, a lawyer who manages the felony unit at the San Francisco Public Defender’s Office, told me he has seen prosecutors’ use of gang enhancements go up in recent years. Young men and women are bundled into the broad category of “gang member” all the time, based on photos like the ones shown at Sebourn’s trial; based on their wearing this color or that one; based, essentially, on a misunderstanding of how difficult these neighborhoods really are for youth. “Posing in a picture, acting cool or acting tough can be a navigation strategy,” Raju said. “That may not mean they want problems; in fact, it may mean the opposite.”