Everyone got into the car, followed by a brief silence.
Zhaxi spoke first, "What if Professor Zhou synthesized those organic phosphorus compounds himself? Then they would only exist in Professor Zhou's laboratory, and the killer might have taken them from there."
Yang Ping looked at him with a smile on his face, a smile that was fleeting.
"You're starting to think like a detective," Yang Ping said, "but you missed a critical question."
Zhaxi asked, "What?"
Yang Ping said, "If those organic phosphorus compounds were synthesized by Professor Zhou himself, how did the killer know about their existence? How did the killer obtain them? And how did the killer know which books Professor Zhou would look through?"
