The man sat stoically at one end of the table, carefully crafting his replies to the FBI agent’s inquiries. He wasn’t considered a major suspect in the murder case. His alibi was believable and he sounded sincere, but the agent pressed on nevertheless. With the suspect’s consent, he was asked a series of questions about the murder weapon: “If you had committed this crime, would you have used a gun?” “If you had committed this crime, would you have used a knife?” “If you had committed this crime, would you have used an ice pick?”
“If you had committed this crime, would you have used a hammer?” One of the weapons, the ice pick, had actually been used in the commission of the crime, but that information had been kept from the public. Thus, only the killer would know which object was the real murder weapon.
As the FBI agent went down the list of weapons, he observed the suspect carefully. When the ice pick was mentioned, the man’s eyelids came down hard and stayed down until the next weapon was named. The agent instantly understood the significance of the eyelid behavior he had witnessed, and from that moment forward the “minor” suspect became the primary person of interest in the investigation. He later confessed to the crime.