Generally, to impeach a witness is to undermine the source of information as opposed to undermining the content of the testimony. The concept is pretty simple really.
The cool thing about impeaching a witness is that it’s a tactic that we’ve been using since we were little kids to win arguments. When someone accused you of doing something on the playground, you probably figured out the fastest way to defend your innocence was to attack the source of the accusation.
Billy: I saw Johnny leave Ms. Johnson a love letter!
Jimmy: No you didn’t four-eyes, you can’t even see two feet in front of your face. How would you even know?
What you’ve done instead of attacking the factual basis of the accusation is attack the witnesses ability to make the statement against you. If Billy can’t see very well, he wouldn’t be able to determine if the love note was actually delivered to Ms. Johnson. In a nut shell, that’s impeachment.
The question now is HOW do we impeach a witness?
An effective way of impeaching a witness at trial is through the use of depositions. What that means is that you use previous statements of the witness to demonstrate inconsistency. If a witness’ story has changed, the jury may interpret that he/she is lying or can’t clearly recall the events for which he/she is testifying.
When a witness makes a statement in trial that is inconsistent with his or her deposition testimony, you must first highlight the question that was answered differently at trial. You will want to make sure that the trial testimony being impeached is a direct inconsistent statement with the deposition given before trial.
Once you have highlighted the statement, you can proceed with the following line of questioning:
1. Mr. Johnson, do you remember having had your deposition taken on January 15, 2009?
2. Do you remember that a court reporter was present at your deposition?
3. Do you remember having been sworn in to tell the truth?
4. Did you tell the truth on that date?
This line of questioning sets the foundation. You are establishing that the witness was deposed previously under oath and that his/her previous testimony was accurate and truthful. After you have set the foundation for the impeachment, then you hit the home run by drawing attention to the inconsistency.
“Do you remember having been asked the following question ___________ and giving the following answer_______.”
What you have done now is drawn the jury’s attention to the fact that the witness has given inconsistent testimony. By asking the previous series of questions you are setting up the witness to contradict himself/herself in way that is easily understood by the jury.
On a previous date you said X, and today you are saying Y. Using the deposition transcript is an awesome tool because it’s transcript of testimony that the witness cannot refute.