REASON #7: Even if you’re innocent, and you only tell the truth in your statement, and you give the police no information that can be used against you, and the whole statement is videotaped, a suspect’s answers can still be used against him if the police (through no fault of their own) have any evidence that any of the suspect’s statements are false (even if they are really true).
Suppose the police have a statement from a witness who claims to have seen the suspect in the area where the crime was committed at the time of the incident. Suppose further that this witness is actually wrong, but has made an honest mistake. The suspect then gives a statement to the police in which he says he was nowhere near the area where the crime took place at the time of the incident. By giving the statement, the suspect has now created a conflict between his own statement and the statement of this witness. By itself, the statement of the witness that he or she saw the suspect in the area at the time the crime was committed is not that useful. But by giving this statement, and creating a conflict with this witness’s statement, the suspect has now made this relatively minor witness into the government’s star witness.
The jury will hear the conflict and will assume that the suspect is lying and wonder why.
So even if you tell the complete truth, you’re putting your cards on the table without first seeing what evidence the government has. And if the government has some bit of evidence which, through some honest mistake, contradicts part of your story, you set yourself up to be portrayed as a liar by giving a statement without first knowing what evidence the government has.