One of the things the drives me nuts about legal dramas on TV or the big screen is how often defendants in trials take the stand and testify in their own behalf. In my experience, defendant testimony is very rare (in the ever rarer situation where a case actually goes to trial), particularly outside of something like a self defense case. The reason why is that testifying opens the defendant up to being questioned about his past.
You see, in most circumstances, a defendant's past criminal record is off limits to the prosecution. The rules of evidence in federal and most state courts prohibit the prosecution from presented that evidence as proof of a "propensity" to commit a crime. In other words, the prosecution can't tell the jury that the defendant is a three-time convicted burglar so he must have committed the burglary he's charged with.
But when a defendant testifies, things change. Any witness can by cross examined to determine their credibility and the weight a jury should give their testimony. Part of that cross examination can include diving into the witness's criminal record. It's the same for defendants. In such situations, judges tell jurors to only consider that information as it goes to the defendant's credibility as a witness, not his general propensity to commit crimes. Does that work?
Apparently not. Over at FindLaw, Sherry Colb writes about a forthcoming study (draft available here) shows that the revelation of prior convictions when a defendant testifies can have an effect on the jury, but not the intended one:
Interestingly, Eisenberg and Hans observed that the jury's knowledge of the prior record did not affect its assessment of the criminal defendant's credibility as a witness. This is an important observation because, as noted above, it is the supposed relevance of prior convictions to the defendant's credibility that provides the legal rationale for permitting the introduction of prior convictions against a testifying criminal defendant, while suppressing the same convictions against a nontestifying criminal defendant.What's the solution? Colb offers several, the most radical of which is to prohibit defendants from testifying at all. That way, jurors would also be prevented from drawing a negative inference from a defendant's decision not to testify.
If, in other words, juries do not in fact consider prior convictions a reflection on a defendant's credibility as a witness, when the convictions have been admitted exclusively for that purpose, then the criminal record apparently plays no legitimate role in the trials at which it is offered. It instead serves, as Eisenberg and Hans conclude, only to lower the jury's threshold for conviction and thus to reduce the burden of proof on the prosecution from "beyond a reasonable doubt" to something less demanding. This diminished burden, in turn, may contribute to the conviction of innocent defendants.
Colb cites olde English common law and some early American law for the premise that defendants at one time were considered "incompetent" to testify because they had a vested interest in the outcome of the trial. But that's been discarded (it used to apply to any interested witness, including the parties in civil cases) and Colb rightly admits being hesitant to silence a criminal defendant.
It's an interesting idea, but one that's not likely to get anywhere. But, I'll admit, I don't have a better one.