“It was terrible,” Mrs. Jacobi was saying to a uniformed officer as Detective Naylor arrived on the scene. “I had just got home from the grocery store and was coming in to ask Simon to help me get the groceries in. I could tell something was wrong the minute I opened the back door, but before I could do anything, someone slapped something over my mouth and nose. The next thing I knew, I was waking up on the kitchen floor. Simon was stabbed to death in the living room – there was nothing I could do, so I called the police right away and waited out here for you to get here.”

“You haven’t touched anything in the living room at all?” the detective asked Mrs. Jacobi. She shook her head firmly.

“I knew that if I touched anything, I might disturb clues, and I really want you to catch the scum that killed my husband!” she said fervently.

“I’m sure we will,” Detective Naylor assured her. He started into the living room to look over the scene of the crime. As he entered, he noticed the victim’s feet sticking out from the other side of the couch, and noted that he was in his stocking feet. It wasn’t until he walked around the end of the couch that he could see Mr. Jacobi, lying on his stomach on the floor. Two uniformed officers stood by, waiting for him to arrive.

“Help me turn him over,” Detective Naylor told one of them. The man was definitely dead. The bloodstain had seeped into the carpet, and soaked the kitchen knife that was hidden under his body. Without a word, he turned and headed back into the kitchen.

“Mrs. Jacobi,” he said, “I’m ready to arrest the scum that murdered your husband. Please stand up and turn around,” he added, unhooking the handcuffs from his belt.

How did Detective Naylor know that Mrs. Jacobi had killed her husband?