Polygraphs are risky. A subject can dope himself up to pass, which is why cops don’t like to administer the test unless they’ve had the suspect in custody for a while. (Unbeknownst to me or the cops, Simpson had already taken a polygraph and scored a minus 22, meaning he failed every single question about the murder. I did not learn this until well after the verdict. Then I shook my head in amazement. It’s hard to imagine that a lawyer would be stupid enough to offer his client up for a second poly after he’d failed the first time.)
