The evidence covered one end of the survey table. Luo laid out the ceramic tag in its envelope, the Registry plate wrapped in cloth, the two survey copies, and Bai’s sealed glass tube. Each had its own place and label.
Gu put the tag beside the notch copied from the central door. The small stamped number fit the mark exactly.
“It identifies a maintenance cycle,” he said. “Not a key.”
“Could the tag have been used to open the door?” Wei asked.
“The number matches the cycle, but the ceramic is fired. It has no teeth or groove that would fit a lock.” Gu pointed to a small line on the central-door sketch. “The door carries the cycle mark. That is what the tag records.”
Luo studied the date. “Two years ago. The response plate carries a Registry seal from the same period.”
“The latest alterations happened after I left the project,” Gu said. “That much is clear. I still can’t say who ordered them.”
Yan looked at the black grit tube. “Can it tell us anything?”
