I asked Officer Chen if they still kept the material evidence from the case. He told me that they were all gone because they thought the case was solved. There was an expiration date on the evidence and it had to be disposed of after that date.

I pulled out the red dress that we bought earlier and showed it to Officer Chen. I asked him if he’d seen it anywhere before.

“Yes, of course I’ve seen it!” he answered without hesitation. “The first victim wore the exact same dress! Where did you get it?”

I told him what happened and what we found. Officer Chen fell into deep thoughts and muttered, “Zhang Qiang... Zhang Qiang… Ah, yes! The first victim was his sister-in-law! Zhang Qiang made that dress for her himself! He wasn’t our suspect, though.”

“Why not?” I asked.

“He had a solid alibi,” Officer Chen explained. “He was with his wife at a hot pot restaurant at the time the murder occurred. They...