The Ohio Supreme Court, in 2000, for example, ruled that someone who had denied all guilt or who would deny all guilt to questions posed could not invoke the Fifth Amendment. That decision was soundly reversed by a unanimous US Supreme in 2001 in Ohio v. Reiner. The Court in that case (which contained Scalia, Thomas, Rehnquist and O’Connor, hardly flaming liberals) reaffirmed that
one of the Amendment’s “basic functions … is to protect innocent men … ‘who otherwise might be ensnared by ambiguous circumstances.” The Court went on to add that “truthful responses of an innocent witness, as well as those of a wrongdoer, may provide the government with incriminating evidence from the speaker’s own mouth. ”
I know what you’re thinking: How can truthful answers from an innocent person incriminate that person? The answer lies in the meaning of “incriminate”; it does not mean to prove one guilty as most folks think.
incrimination of oneself; specifically:
the giving of testimony which will likely subject one to criminal prosecution”
(emphasis added by [author]).
So that it is an innocent person who might be wrongfully prosecuted through his own testimony that the Amendment tries to protect; not a criminal with something to hide. In fact, the Supreme Court views very expansive protection under the Fifth. In Hoffman v. United States, the Court held that The Fifth does not protect just potential answers to questions that may be enough to support a conviction (“I shot him”, for example) but in fact “embraces those which would furnish a link in the chain of evidence needed to prosecute the claimant.” That’s the ticket:
the testimony need only furnish a link needed not to convict but merely to prosecute the potential defendant.
http://www.courtroomstrategy.com/2010/04/on-taking-the-fifth/