Chapter 2083: Chapter 1791: This Is the Kind of Case We Fear Most

On Friday morning, Dr. Yuan called again. Yang Ping called Zhaxi to the office and turned on the speakerphone.

"Professor Yang, the test results for the book pages are out." Dr. Yuan’s voice had a restrained excitement. "We found traces of organophosphates on some of the books on the deceased’s bookshelf. The concentration isn’t high, but they are indeed present. Moreover, we also detected residues of toluene and xylene on the pages of these books."

Yang Ping’s breathing paused for a second: "Which books?"

"Mainly those on the second row of the bookshelf, about twenty or so. They’re all chemistry books, some are textbooks, and some are monographs. Each one has residues, but the concentration distribution is uneven, with the highest concentration at the edges of the pages and lower concentrations in the middle."

Yang Ping asked, "What about the fingerprint test results?"

"Those are out too. We found traces of organophosphates and toluene on the fingerprints of the deceased’s right index and middle finger. The amounts are minimal, but it’s enough to prove he had contact with these substances."

Yang Ping was silent for a long time, then he spoke a sentence softly, but Zhaxi could hear how heavy it was: "Someone tampered with those books." 𝒻𝘳𝘦𝘦𝘸ℯ𝒷𝘯𝘰𝑣ℯ𝑙.𝘤𝑜𝘮

On the other end of the line, Dr. Yuan asked, "Professor Yang, who do you think did this?"

This should not have been a forensic issue and should have been up to the investigative officers, but Dr. Yuan was also very curious and wanted to follow Yang Ping’s line of thought to continue analyzing.

Yang Ping did not answer directly but asked, "Besides Professor Zhou, who else would read those books?"

Dr. Yuan said, "We are investigating. So far, what we know is that Professor Zhou’s study is usually locked, and only he had the key. His students said he never allowed anyone into his study."

Yang Ping said, "That means, to access those books, it had to be either Professor Zhou himself or someone who could get the key. Professor Zhou wouldn’t poison his own books, so the culprit must be someone who could get the key."

Dr. Yuan said, "Understood, we are checking all who might have accessed the key or given him books."

After hanging up, Yang Ping leaned back in his chair and closed his eyes.

Zhaxi couldn’t help but ask, "Professor Yang, why would the murderer use such a complicated method? Why not poison directly?"

Yang Ping opened his eyes and looked at him: "Because direct poisoning would be discovered, poison in tea or food would show up in an autopsy. But using this method, the poison is absorbed slowly and in small amounts through the skin over time, making it hard for an autopsy to trace the source. If we hadn’t noticed how clean those books were, if Dr. Yuan hadn’t noticed the pigmentation on the fingertips and consulted us, this case might have been classified as a natural death."

He paused and continued, "Also, this method of murder requires the perpetrator to have deep knowledge of chemistry, to understand the toxicity mechanism of organophosphates, the penetration-promoting effect of organic solvents, and which books Professor Zhou would frequently read. This is not something an ordinary person could do."

Zhaxi now very excitedly said, "Are you saying the murderer might be someone from the chemistry department?"

Yang Ping didn’t answer, but his silence itself was the answer.

In the afternoon, after Zhaxi finished his work, he reorganized all the clues from the past few days.

He drew a timeline in his notebook, much like organizing a patient’s medical history:

Half a year ago: Professor Zhou began losing weight and becoming withdrawn, blood cholinesterase started to drop (3800).

Four months ago: Blood cholinesterase dropped to 2100, pigmentation began appearing on fingertips.

The past week: Received a threatening letter.

Three days ago: Death occurred! Pupils severely constricted, pigmentation on fingertips, a trace of organophosphates in the teacup, and residues of toluene and xylene on the shirt cuffs.

Yesterday: Book pages tested positive for organophosphates, toluene, and xylene, and fingerprints showed trace residues.

He connected these clues to form an initial hypothesis:

Someone applied a solution of an organophosphate compound dissolved in toluene/xylene onto the chemical books Professor Zhou frequently read. Each time he flipped the pages, his fingertips would contact this solution. The organic solvent disrupted the skin barrier, allowing the organophosphates to penetrate the skin. Long-term exposure led to chronic organophosphate poisoning—weight loss, personality changes, continuous decline in cholinesterase, and fingertip pigmentation. At some point, a larger dose from perhaps prolonged reading led to acute poisoning, severe pupil constriction, respiratory depression, and death.

The trace of organophosphates found in the teacup might be from pesticide residue already in the tea leaves and unrelated to the case, an oversight even by the murderer.

If this hypothesis holds true, the culprit must meet several criteria:

First, have access to the key to Professor Zhou’s study or the books. Second, have sufficient chemical knowledge to understand the toxicity of organophosphates and organic solvents. Third, have a means to obtain organophosphate compounds and organic solvents. Fourth, be familiar with Professor Zhou’s reading habits and know which books would be frequently read. Fifth, have a motive.

The first four conditions point to the same kind of person, someone around Professor Zhou, particularly someone from the chemistry department.

Zhaxi wrote this hypothesis in his notebook.

Who is the murderer?

Zhaxi’s curiosity was piqued; he increasingly felt that this kind of deductive reasoning was extremely fascinating.

On Friday afternoon, Zhaxi took the organized hypothesis to Yang Ping. Yang Ping sat at his desk, turning the pages of Zhaxi’s notebook slowly. He spent a long time on each page, sometimes pausing to think, sometimes furrowing his brow.