The second piece of evidence came from where they least expected it: a box Sasha's mother had been meaning to donate to the school for years, filled with old event programs and photographs from a decade of PTA fundraisers she'd helped organize.
"I wasn't even looking for this," Sasha said, spreading a handful of old photographs across the treehouse floor. "My mom just handed me the box and said 'give this to whoever wants old junk.'"
One photograph, dated the same year as the note, showed a faculty gathering — Callahan among a group of teachers, and beside him, unmistakably, a much younger Marissa Cole in what looked like a student-volunteer shirt, standing closer to him than the group photo composition really required.
On the back, in handwriting Nathan now recognized instantly, someone had written a date and a short note: Spring fundraiser — M helped set up, stayed late again.
"Stayed late again," Sasha repeated. "As in, this wasn't a one-time thing."
Nathan turned the photograph over again, studying the easy, practiced smile on Callahan's face — the same smile Nathan had seen in the hallway just days ago, aimed now at him and Sasha with exactly the same warmth it had once aimed at a seventeen-year-old volunteer a decade ago.
It made his skin crawl in a way the note alone never had.
"We have his handwriting matching a pattern," Nathan said slowly. "We have a timeline. We have Marissa's reaction. It's still not enough for anyone official to act on — but it's not nothing anymore, either."
"So what do we do with it?"
Nathan looked at the photograph, then at Sasha, then at the growing folder between them that had started as a single scrap of paper and had somehow become something that felt heavier every day.
"We have to decide how far we're willing to go," he said quietly. "Because I don't think this ends with just us knowing anymore."
Sasha didn't answer right away. And that silence, more than anything else that had happened so far, told Nathan they were standing right at the edge of something neither of them could take back once they crossed it.
"If we take this further," she said finally, "there's no going back to just being two kids who found an old note. We become the two kids who tried to expose a teacher. That follows us. Maybe for the rest of high school. Maybe longer."
"I know."
"And if we're wrong — if we've built this whole theory on a handwriting match and a few too-close photographs — we could ruin someone's life for nothing."
Nathan turned the photograph over again in his hands, studying the inscription on the back, the easy, practiced smile in Callahan's face that no longer looked warm to him at all. "I don't think we're wrong," he said quietly. "I wish I did. It would be a lot simpler if I did."
"Yeah." Sasha exhaled slowly, some of the tension leaving her shoulders even as new resolve settled into its place. "Me too."
They sat with the evidence between them a while longer, the weight of the decision settling over both of them like something almost physical — heavier than either of them had expected, back when this had just been an interesting old note behind a drawer.
"Whatever we decide," Sasha said eventually, "we decide it together."
"Together," Nathan agreed, and meant it more than he'd meant almost anything else that year.