How To Prove a Witness Is Lying?

Updated December 18, 2023
8 min read
How To Prove a Witness Is Lying?


As an attorney, it is up to you to do everything you can to solidify your case, and in some cases, figuratively, that means proving a witness is lying. But how can you tell and what is the best way to expose a liar in court?

How To Tell if Someone Is Lying in Court

As an attorney, being able to determine if someone is lying in court can provide you with the circumstances you need to overturn a conviction or have charges dropped for a crime on behalf of your client. Instead, what tends to happen is that the exposure of the lie and the intended goals behind lying give you, the attorney, the leverage you need to request that the charges be dropped or that the intended consequences be reduced for your client.

If you can determine that a witness is lying and you can get them to explain why they lied about the incident, it will give your case a great amount of ammunition.

How To Expose a Liar in Court

During a trial, the purpose of your cross-examination is to get testimony from any witnesses that will strengthen your side of the case and to challenge any weaknesses. If you are able to prove there was a lie, especially if that lie relates to a central fact that is currently being disputed, you can discredit the witness by proving the witness lied and continuing with your line of questioning until such time as you get to the reasoning behind why the witness lied. You might also consider presenting an affidavit — a written statement confirmed by oath or affirmation of the witness — and present it in the court to reveal inconsistencies in the witness's testimonies.

Why does the ‘why’ matter?

How To Prove Someone Is Lying in Court

Because the only thing you do is submit a line of questioning that attacks the witness, it doesn’t necessarily expose the thought process behind the lie, what motivations the witness had, and what they were trying to achieve by lying.

For example, imagine a government-employee driver hit a pedestrian who was legally in the crosswalk while the driver was making a left turn. After leaving the accident, the driver took the truck back to the government depot and filled out the official accident report. Even though he knew that he had never seen the pedestrian in the crosswalk before he hit the pedestrian, he wrote something else in the report stating that the pedestrian ran out from between two parked vehicles, tripped over the sidewalk, and fell under the tire. However, this driver did not realize that a traffic camera at the intersection recorded the entire thing.

In this example, as the attorney, you could prove the lie by asking if the driver knew there was a video camera. When the driver says they did not, you can state that they lied in the accident report and ask them if this is correct. This is a very fast way to get to the truth and prove a witness is lying, but it doesn’t make the most out of the potential impact on the case.

The Right Way To Prove Someone Lied in Court

Instead, a more comprehensive line of questioning will help you to develop why the driver created that lie, what choices they made when they decided what they were going to lie about, and what they wanted to achieve by telling the lie. This will not only prove a witness is lying but serve as a way to compel the judge or jury and win the argument.

The use of a legal citation maker while preparing before the court can empower you with the needed laws and codes for use in building the case or citing as part of in-court documentation. You need to ensure everything is prepared thoroughly before the court proceeding, and using the citation maker is what can help you stay assured the information is from trusted and reliable sources.

As a lawyer, the way for you to prove a witness is lying, and to get to the truth in court, you need to go about the witness’s testimony and the criminal proceedings a little differently.

If you consider the example above of the trucker and the accident, you should carefully incorporate certain words into your line of questioning, such as:

  • Deceive;

  • Fraudulent;

  • Obstruct;

  • Manipulate; or

  • Tell less than the truth.

These are words that you want to deliberately and patiently incorporate throughout the course of your questioning to prove someone is lying. 

  • Instead of simply asking your witness if they knew there was a camera, you might consider asking them if they are trained by the company to look for pedestrians and if they are trained on how to properly fill out an accident report. 

  • Once they confirm, you can ask if they are trained to fill those reports out barely. 

  • Then, ask if they were trained to fill out accident reports completely. 

  • Ask if they were given an education by the company on how to document what they observed in those accident reports. 

  • Ask them if they were trained by the company to record facts no matter who those facts hurt or help.

  • Once they confirm, you can ask them if they were trained by the company to never report things that they did not see or to never make up facts. 

  • Again, once they confirm, you can ask if it’s true that they would never put fraudulent information in the report.

These are the first steps, a line of questioning that establishes the education received from the company as it pertains to filling out an accident report. This lays the foundation.

Thereafter, you can focus on the thought process behind telling the lie. Comparing or contrasting different choices can be a great way to get a witness to explore the reason why they told a lie.

  • For example, ask them if, on the drive back to the depot, they thought about what happened in the accident.

  • Follow up by asking whether they thought about what they would write in the report ahead of time.

  • Ask them if they had a choice to make before they filled out the report, a choice to be less than honest or honest.

  • Follow it up by asking whether they had a choice to be truthful or deceptive, helpful or obstructive.

  • Ask them if, during the course of their return to the depot, they decided they were going to write something that was less than the truth.

After that, you want to focus on things like the motives for this dishonesty and the willingness of the witness to lie.

For example, you can ask them if they were concerned about losing their job or being disciplined as a result of the accident and whether they chose to put fraudulent information in the report.

As an attorney, you can leave the witness to even more areas of questioning, during which time the judge or jury is given the opportunity to come to their own conclusions, to see that the witness is a liar, and to recognize why the witness lied. Your job isn’t to outright call them a liar in court or on the record but instead to focus on their conduct, their actions, and their choices. Being able to successfully probe through the lie and explore the motivations and the decisions that went into that will discredit the witness and the adversary.

What Happens if a Witness Lies in Court

If a witness lies in court, they can be convicted of perjury. Most of the time, this is not going to happen, but the judge does have the authority to put them in jail for a short time frame as a result of breaking the law.

Final Thoughts

As an attorney working a criminal defense case or any other criminal case, any statement or evidence provided by an expert witness or any other type of person can make the difference between a conviction on multiple charges and winning your case. The best legal advice for attorneys is to be patient and deliberate while trying to expose a witness for lying.

Article by
Yevheniia Savchenko

Yevheniia Savchenko is a Product Content Manager at Lawrina. Yevheniia creates user interface copies for Lawrina products, writes release notes, and helps customers get the best user experience from all Lawrina products. Also, Yevheniia is in charge of creating helpful content on legal template pages (Lawrina Templates) and up-to-date information on US law (Lawrina Guides). In her spare time, Yevheniia takes up swimming, travels, and goes for a walk in her home city.

If you have any questions or suggestions regarding the product or UX content for Lawrina, feel free to contact Yevheniia directly at or connect with her on LinkedIn.

Frequently Asked Questions

What are some effective strategies to unmask a liar in a court setting?

Typically, this involves highlighting inconsistencies between the witness's testimony and the known facts of the case, searching for contradictions in their statements, looking for objective evidence that refutes their claims, or presenting other testimonies that contradict the one in question.


What is the appropriate method to demonstrate in court that someone lied?

The proper way to establish that someone lied in court typically involves gathering clear, credible evidence that contradicts the person’s statements. It also necessitates presenting this evidence neatly and logically and questioning the witness on the stand specifically about the contradicting points.


What are the consequences if a witness is found to have lied in court?

If a witness is found to be lying in court, they could face severe penalties like charges of perjury, that is, lying under oath. Penalties for perjury can include fines, imprisonment, and it can also significantly harm the credibility of the witness.