The term impeachment has to do with challenging a witness related to their testimony against a criminal defendant. There are different ways to impeach a witness. One form of impeachment is called extrinsic impeachment, which basically has to do with impeaching a person with evidence that's outside their testimony or outside of the allegations in a particular case. Extrinsic impeachment is very effective to show that a witness is not telling the truth and has a tendency to lie or distort the facts. So, this form of extrinsic impeachment has to do with asking the witness about a collateral issue and then bring forth evidence to show that they're not telling the truth about that collateral issue and therefore, their testimony is unreliable, not credible.
An example of extrinsic impeachment would be a situation where a witness is testifying and then make some remark regarding well, I've never lied in the past, so why would I lie this time? Now, if you have evidence that shows they have lied in the past – for example, let's say they made that statement and they committed perjury before in a completely separate instance – well now you could certainly use that perjury case to extrinsically impeach them. You can say, wait a minute, two years ago you were on the witness stand testifying just like you are now and you lied about some material fact and you were convicted of perjury. Right? Now, no matter what they say to that, you've got the proof through court documents that they were convicted of perjury. You've destroyed them through extrinsic impeachment.
Extrinsic impeachment is not always that easy though to get somebody with in a criminal case in Los Angeles, because a lot of times the prosecutors will object and say that it's not relevant. It has nothing to do with the current case. That's why it's so important that the witness is foolish enough to fall into the trap and say something. We just did a case in downtown Los Angeles – 210 West Temple – and during the preliminary hearing I asked the witness whether they had ever been involved with beating somebody up outside the same bar that they got in the altercation with my client. My client won that fight, so my client was being charged with battery and great bodily injury. The witness was foolish enough to say, no I've never had any problems before. Meanwhile, we had a video of them beating somebody up outside the bar. Very similar circumstances to my client. That video came in to impeach them. That's great stuff right there. That's where you just destroy the credibility of the witness and as the witness' credible goes, so too does the prosecutor's case in one of the Los Angeles courthouses.
Now, there's also what I would characterize as intrinsic impeachment, which basically has to do with impeaching the witness right on point with whatever it is they're testifying about – even with their own testimony. This happens all the time in criminal defense where a witness says something during their direct examination by the prosecutor, and then on cross-examination, they say something completely different and you say, wait a minute, you just testified when the prosecutor was asking you questions to this, and now you're changing your testimony.
Another good form of impeachment that I use all the time in a criminal case in Los Angeles – that typically occurs at the trial is, usually there's been a preliminary hearing already or the witness has already testified under penalty of perjury, and now here they are again testifying at the trial. If they say something different than what they said at the preliminary hearing, that's the best impeachment because both scenarios are under penalty of perjury, they're on the witness stand at the time and that's when you can really get them – to be able to bring the entire testimony up, impeach them, ask the judge to take judicial notice of the preliminary hearing, explain it to the jury, explain it to the witness. Wait a minute – didn't you testify under penalty of perjury a few months ago at a preliminary hearing and we asked you a very specific question – and now look, you're changing your testimony. Now you've got the witness. Now you can really dig in and destroy their credibility through effective impeachment. It's one of the most important terms in LA County when it comes to good criminal defense work.
A lawyer must know how to impeach a witness or know how to discredit a wittiness who is clearly lying. Without this ability, they're not effective and cannot really do damage to their testimony and hence, damage to the prosecution's case.