When any witness, including a defendant, testifies, his or her credibility is at issue. The fact-finder (either judge or jury) must decide whether and how much to believe the witness. That’s why courts allow into evidence certain kinds of past convictions—to aid the determination of how trustworthy the witness is.
Generally, prosecutors can't use evidence of prior convictions to prove a defendant’s guilt or tendency to commit crimes, but they can sometimes use them to question the truthfulness or credibility of the defendant’s testimony.
Courts won’t admit evidence of any old conviction to impeach a witness. Rather, the crime must typically be either a felony or an offense involving dishonesty, whether a felony or misdemeanor. Some states don’t allow judges to admit any information regarding prior convictions unless the defense has first offered evidence to establish the defendant’s credibility.
Prosecutors can usually use evidence of actual convictions only. They can’t ask the defendant-witness about pending charges or arrests that didn’t result in convictions. But they can ask testifying defendants about convictions that are currently pending on appeal or for which sentence hasn't yet been imposed.
Unfair to the Defendant?
Judges will weigh, on the one hand, the value of the evidence of a prior conviction in helping the jury determine the defendant’s credibility against, on the other, possible prejudice. Judges must take into account the possibility that jurors will presume the defendant guilty if they learn about his or her past crimes.
In deciding whether to admit evidence of a prior conviction, courts consider the following factors:
- the type of crime
- whether the crime indicates that the defendant is untruthful
- how much time has passed since the conviction (convictions that happened 10 years or longer ago are often inadmissible)
- the length of imprisonment, if any
- the defendant’s age at the time of the conviction
- whether the defendant’s credibility is central to the current case
- the importance of the defendant’s testimony in the current case (the defendant may refuse to testify if evidence of the prior conviction will come in), and
- the defendant’s conduct since the prior conviction.
Judges usually consider evidence of prior convictions for the same or a similar crime (as the one the defendant now faces) very prejudicial. For this reason, courts in many states won’t admit very similar prior convictions if the prosecution can use a different prior conviction to impeach the defendant.
Courts are more likely to admit evidence of crimes involving dishonesty than crimes of violence or those similar to the offense being tried. Federal courts and some state courts automatically allow evidence of prior crimes involving dishonesty without any prior determination of prejudice.
Priors in Action
Consider the following examples, which show how judges determine whether to admit prior convictions of testifying defendants:
- A defendant is charged with murder and has a prior conviction for passing bad checks. Because the prior conviction involves a crime of dishonesty, the judge will probably allow the prosecutor to question the defendant about it.
- A defendant is on trial for murder and has previously been convicted of the same. Because the prior crime is identical to the charged one, the court will determine whether evidence of it will be too prejudicial to the defendant. The risk is that the jury will believe that a defendant who murdered once must be guilty if charged again.
- The charge is theft (from an employer); the court allows evidence of the defendant’s prior conviction of passing bad checks because the crimes aren’t substantially similar. Passing a check while knowing that it won’t be paid isn’t the same as swiping an employer’s cash receipts. The judge didn’t act improperly by admitting evidence of the bad-check conviction. (State v. Russell, 382 S.W.3d 312 (Tenn. 2012).)
Consult a Lawyer
If you face criminal charges, consult an experienced criminal defense lawyer. Only such an attorney can properly advise you about your chances at trial, represent you at trial, and analyze the pros and cons of you testifying (including the chances of a prior conviction coming into evidence).