When the police question you, they’re going to carefully note what they have told you and what they haven’t. Any new facts you mention will be used as evidence that you have firsthand knowledge of the crime, but psychologically speaking, it’s nearly impossible to remember exactly what the police have told you. For the same reason that eyewitness testimony is suspect, people employ gap-filling when they encounter new information. They make reasonable inferences based on what they know or have been told and extrapolate further.
For example, let’s say the police tell a suspect during a murder investigation that neighbors heard shouting and some sort of scuffle and then a series of loud bangs. Many people would interpret those loud bangs in their mind as gunshots, but the police haven’t mentioned anything about a weapon, a gunshot, or bullets. As soon as the suspect mentions gunshots, the police will use that as evidence that the suspect had firsthand knowledge of the murder. In court, the police officer and prosecutor can make a convincing display for the jury. A talented prosecutor will build tension in the courtroom leading up to this moment. She will ask the police officer, “Is there anything about the defendant’s statement that confused you or interested you?” The officer will answer matter-of-factly, “I never said anything about a shooting or a gun. I said we were investigating a murder.”
It’s nearly impossible to keep straight what the police have told you, and this holds true even if the police are investigating you for a petty misdemeanor instead of murder. Intelligent people are possibly more susceptible to gap-filling because the more intelligent a person is, the more inferences they will draw. All of this can be avoided if you simply refuse to talk to the police without your lawyer present.