If what you mean by evidence is "your mouth," then you will have to testify in court if you are subpoenaed. But you do not have to speak to law enforcement outside of court, unless you choose to. One exception to your testimony in court is the 5th Amendment, where if what you say could incriminate yourself in another crime, then you can "take the 5th" and remain silent on any given question the answer of which could incriminate you.
Answered on Aug 28th, 2012 at 10:38 AM