Kevin lures nine students to the gym with the intention of murdering them: Greer Ulanov, Denny Corbitt, Jeff Reeves, Laura Woolford, Brian "Mouse" Ferguson, Ziggy Randolph, Miguel Espinoza, Soweto Washington, and Joshua Lukronsky.
At first glance, these students don't have anything in common. They're quite a diverse group—Kevin is an equal-opportunity mass killer. He wants to murder the outcast kid, the geeky kid, the pretty kid, the Latino kid, the black kid, the gay kid, and so on. It's like Kevin wants to put everyone in a state of fear. Anyone could be next.
The more Eva thinks of the victims, though, the more she comes to a different conclusion: that all of them had something they were passionate about, whether it be theater, dance, or basketball. Each victim had something he or she could deem as his or her favorite. And Kevin, being incapable of enjoying life, wanted to destroy that. Kevin gets joy from "despoil[ing] other people's pleasures" (21.115), but eventually that isn't enough for him. Instead of destroying the pleasure, he decides to destroy the person.
Also included in the slaughter was English teacher Dana Rocco. Maybe Kevin kills her because his mom likes her. Or maybe he kills her because she actually understands him, and he makes every effort to remain misunderstood. Despite Kevin being a jerk, Ms. Rocco doesn't actually hate him. She tells Eva, "You tell him I'm onto him" (25.86)—but not as a threat. She seems to admire Kevin's intelligence and wants to help him in a way. She isn't scared of him. So Kevin feels the need to prove her wrong and make her feel scared.
Kevin also kills a cafeteria worker who ends up in the gym, which is the wrong place at the wrong time. Kevin has no qualms about racking up a double-digit body count.