“I remember that he was kind to me on my first day of school, when I didn’t know anyone. I remember how he was the only one who stood up for me when a lot of people turned on me.”

“That was Arthur.” His name trembled on her lips. “He wasn’t a monster.”

“I know,” I said, not sure if this was a lie or not.

The thing that everyone said Arthur was—I do believe it. But the report Dr. Anita Perkins submitted to the police acknowledged that even psychopaths can show flickers of real emotion, genuine empathy. I like to believe he experienced some for me, even though Dr. Perkins rated Arthur using the Hare test, a twenty-item inventory of personality traits and behaviors used to detect psychopathy, and Arthur scored off the charts.

So much of what Arthur did for me, the protective brother act and even that nonsense he sputtered at the end, the knife handle extending from his chest perfectly parallel to the floor, “I was only trying to help,” was either an imitation of kindness or careful, chilling manipulation. Dr. Perkins wrote that psychopaths are particularly skilled at identifying a victim’s Achilles’ heel, and profiting from it in a way that suits their purposes. When it came to pulling off the ultimate con, forget Nell, Arthur was my original study.

Ben was depressive, suicidal, not necessarily predisposed to violence the way Arthur was, but not opposed to the idea either. He and Arthur had traded violent fantasies about taking out their idiot classmates and teachers all through middle school. It was always a joke for Ben—Arthur was just waiting for something to happen that would make him seriously consider turning fantasy into reality.

That something was Kelsey Kingsley’s graduation party. The humiliating thing that Dean and Peyton did to Ben in the woods that drove him to his first suicide attempt. According to Arthur’s diaries, he broached the idea of an attack, “a Bradley Columbine,” when he visited Ben in the hospital not two weeks after his ragged wrists landed him there. In his diary he wrote how he had to wait for the nurses to change shifts, when they would finally have a few moments of privacy, and it was so annoying. (“What are we, two helpless fucking babies?”) His father had a gun, the beginning of their arsenal. Arthur could get a fake ID, pose for eighteen—he looked older than his age already. There were instructions on the Internet for building a pipe bomb. They were smart, they could really do this. His instinct told him that Ben had snapped, turned a corner he would never retrace, and it was spot-on. Ben had nothing to lose because he wanted to die. If that was going to happen, he might as well make those guys pay for what they did to him.

The media narrative concluded that Arthur and Ben were bullied—for being weird, for being fat, for being gay. But the police reports tell a much different story, a truth that has nothing to do with bullying, the cause du jour. Although it’s widely accepted that Arthur was gay, Ben wasn’t. That thing Olivia said she saw, Arthur giving Ben a blow job at the Spot? That was a lie—desperate, stupid teenage gossip that tragically, ironically, made the fire dance higher. The rumor infuriated and hurt Ben, and Arthur pounced. “I promised him Olivia,” Arthur wrote in his diary, the first blithe mention of a hit list. Only Arthur didn’t care about a hit list, not really. The attack wasn’t just about getting back at his tormentors, or about revenge, it was about his contempt. He was after anyone who was intellectually inferior to him, which was everyone, in his mind. He proposed the idea of a list only to tantalize Ben. His goal had been to take out the entire cafeteria with his bombs—the Shark, Teddy, the sweet lunch lady who built his sandwiches, cheese layered between the roast beef and ham, just how he liked it—we were all fair game. He hid out in the empty dormitory rooms on the third floor of Bradley, waiting for detonation so he could go downstairs and savor the carnage before he ended his own life. The cops would shoot to kill anyway, and a psychopath’s worst nightmare is relinquishing control. If he was going to die, it would be on his terms. He started shooting when he saw that only one of his amateur bombs went off, inflicting “minimal” damage.

There was a part in Dr. Perkins’s report, which was available for the public to read, that I started in on and only when I realized it concerned me did I double back and reread the first few paragraphs. It was like seeing a picture and not recognizing yourself caught in the frame—who is that salty girl frowning in the background? Doesn’t she know it gives her a double chin? The meta-moment of experiencing how the rest of the world sees you, because the salty girl is you.

Dr. Perkins classified Arthur and Ben’s “partnership” under the dyad phenomenon, a term criminologists coined to describe the way murderous pairs fuel each other with their bloodlust. Between a psychopath (Arthur) and a depressive (Ben), the psychopath would most definitely be in control, but as a psychopath craves the stimulation of violence, a hotheaded partner can provide an invaluable service: riling him up for the slaughter. Arthur and Ben planned the attack for six months, and for almost that entire time Ben was confined to a mental rehabilitation center, putting on a show for the doctors and nurses to convince them he was no longer a threat to himself. In the meantime, Arthur found himself a new cheerleader, someone whose pain and anger padded the void of violence. This sidekick kept him on a low simmer until he finally had the opportunity to boil over. She didn’t name me, but there was no one else it could have been. Sometimes I wonder what would have happened if I hadn’t set Arthur off the last time I saw him in his room. If he was gearing up to tell me about his plan. Ask me to be a part of it.

“This was at the shore too.” Mrs. Finnerman smoothed a wrinkle in the plastic. I was surprised to see Mr. Finnerman, elbows draped over the back of a bench on the boardwalk, roily black curls springing out of his tan chest. Next to him, Arthur standing, pointing to the sky and shouting something, Mrs. Finnerman’s flimsy arms anchored around his legs to keep him from falling.

“How is Mr. Finnerman?” I asked, politely. I have the picture that immortalizes one of his most intimate moments with his son, and still I’ve never met the man. He surfaced on the Main Line when everything happened, of course, but faded away shortly after the funeral. The funeral. Yes, killers need to be buried too. Mrs. Finnerman humiliated herself calling rabbi after rabbi, desperate to find someone who would be willing to perform the service for Arthur. I don’t know what Ben’s family did. No one does.

“Oh, you know,” Mrs. Finnerman said. “Craig’s remarried, so.” She took a sip of cold tea.

“I didn’t know that happened,” I said. “I’m sorry.”

“Yes, well.” There was a speck of tea in the valley of Mrs. Finnerman’s upper lip. She didn’t brush it away.

“You know,” I said, “I have a photo of Arthur and Mr. Finnerman too.”

The living room suddenly burst with light, the sun pushing a cloud out of the way, and Mrs. Finnerman’s pupils retracted. I’d forgotten her eyes were blue. “Excuse me?”

I risked a glance at Aaron. He was guiding a microphone around the room, oblivious to what I’d just triggered.

I clasped my hands around the coffee mug, lukewarm now. “I have this picture . . . um, Arthur used to keep it in his room.”

“The one with the seashells?” Mrs. Finnerman wanted to know.

“Of Arthur and his dad.” I nodded. “Yeah.”

All the softness in Mrs. Finnerman’s face was gone. Even her wrinkles didn’t look so much like folds of skin as they did hard cracks in a pane of glass. “How do you have that? I’ve been looking for it everywhere.”

I knew I had to lie, but it was like someone had taken an eraser to my mind. I couldn’t think of any way to answer her that wouldn’t upset her. “We got into a fight,” I admitted. “I took it. It was mean. I was trying to upset him.” I stared into my cold cup of coffee. “I never got a chance to give it back.”