Frequency and Success: An Empirical Study of Criminal Law Defenses, Federal Constitutional Evidentiary Claims, and Plea Negotiations

Discussions of criminal law defenses typically focus on policy issues, with pundits, lawmakers, and scholars each advocating different grounds for allowing various defenses. While the insanity defense and plea negotiations have been the subject of intense philosophical and statistical scrutiny, most defenses have simply been accepted as part of the system without any empirical examination of their use. This survey of prosecutors, judges, and defense attorneys investigates the frequency and success rates of six defenses (entrapment, statutes of limitations, double jeopardy, diplomatic immunity, insanity, and reasonable mistake of law), three constitutional evidentiary provisions (the Fourth Amendment search and seizure exclusionary rule, the Fifth Amendment Miranda rule, and Sixth Amendment faulty identification procedures), and plea negotiations.