One night around dinnertime, Kruse Wellwood sent an instant message to Kim Proctor. “Hey, I thought you had babysitting,” he wrote. “Did you finish early?”

Gawky and boyish, 16-year-old Kruse had scraggly brown hair and uneven eyes. He lived in a bungalow with his mother on Happy Valley Road, a leafy street in the small town of Langford, British Columbia. On this evening, as on so many others, he was hanging out with his best friend, Cameron Moffat, a burly 17-year-old goth. But, like many kids his age, Kruse spent as much of his time with friends online as he did in person. When he wasn’t texting, he was playing World of Warcraft, the online role-playing game, or chatting over the Microsoft network with friends.

When Kruse IM’d Kim to see if she was done babysitting, no response came. But he didn’t expect one. The instant message was a cover. Kruse knew Kim had never made it to her job. She was right there in his house with him and Cam. Bound. Beaten. Raped. And, by the next morning, stuffed in his freezer. Dead.

Everyone knows teens live with abandon online—exposing their secrets, likes, dislikes, sexual preferences, home addresses, phone numbers, and so on—in ways their parents can’t understand. But it’s not just this generation’s sense of privacy that’s eroding. It’s their sense of permanence. They act as though the words they write and pictures they post and texts they send vanish into the ether. But in fact they’re leaving a running transcript behind, a digital trail of their hopes, their anxieties, and, in the case of at least one small Canadian town, even their crimes.

Kimberly Proctor was born on January 1, 1992. Her middle-class parents—Lucy, a Walmart manager, and Fred—a diesel mechanic, called her “Baby New Year” or Kimmy. Kim had a passion for animals, raising a menagerie of lizards, rabbits, mice, and hamsters. She loved cats so much that, when she was young, she wore cat ears to school.

But Kim’s earnestness made her vulnerable. Kids teased her about her cat ears, meowing at her in class, and never let up as the years went on. “She was bullied throughout her life,” her mother recalls. Kim’s attention-deficit disorder didn’t help. She would panic navigating the swarm of students in the hallways at school. Her parents tried to medicate her, but this only “zombied her out,” her mother said. Eventually, they transferred her to an alternative school, Pacific Secondary, to get more individualized attention.

The school attracted a variety of troubled kids in Langford, a sleepy suburb of Victoria, but few more troubled than Kruse Wellwood. Kruse was a killer’s son. In 2001, following his involvement in a sexual-assault case, Kruse’s father, Robert Raymond Dezwaan, sexually assaulted and murdered a 16-year-old girl. Dezwaan was sentenced to life with no possibility of parole for 15 years. Kruse later said he clearly understood what his father had done, but he seldom discussed it. Kruse had been involved in a variety of incidents—from smoking pot to stealing money from mailboxes—by the time he was 16.

Kruse and Cam met in fifth-grade art class when they bonded over their mutual disdain of a teacher. While Kruse was wiry and intelligent, Cam was a hulking slow learner who suffered from A.D.H.D. A psychiatric report later revealed that Cam had been sexually abused at age four (although it was not publicly revealed by whom). As a child, Cam began jumping out his bedroom window at night until it was barred. Cam resisted counseling and meds. He began lashing out at home and cutting himself to relieve stress. He was increasingly menacing at school too, bringing a knife to class.