Last Updated on July 9, 2025
Criminal cases are based on evidence. Because the U.S. Constitution guarantees that defendants are innocent until proven guilty beyond a reasonable doubt, the evidence presented by the prosecution must be enough to outweigh that offered by the defense. Not everything can be used as evidence though, and many rules determine the admissibility of evidence in court. This guide can help you better understand the difference between what is admissible vs. inadmissible.
What is Admissible Evidence?
Quite simply, admissible evidence is anything that can be used to help prove the prosecution or defense’s case. There are many types of evidence, including witness testimony, documents, demonstrative evidence (such as photos, x-rays, videos, audio recordings, or charts), and physical evidence (like bullet casings, blood samples, or clothing).
What Makes Evidence Inadmissible?
Anything that cannot be legally introduced as evidence in court is considered inadmissible. Essentially, it refers to evidence that is considered unreliable for one reason or another.
Inadmissible Vs. Admissible Evidence
The three factors that matter the most when determining what makes evidence admissible or inadmissible are whether it is:
- relevant
- reliable
- legally obtained
Depending on the situation, these issues are frequently subjective, which is why it is so important to always work with a skilled attorney when attempting to fight criminal charges.
What Makes Evidence Irrelevant?
The relevance of evidence is often debated between the prosecutor and the defendant’s criminal defense lawyer, and the judge must decide what can be considered relevant enough to be used as official evidence.
Whether someone being tried for reckless driving was previously accused of underage drinking, for example, would likely be considered irrelevant and, thus, inadmissible because one crime is unrelated to the other. On the other hand, if someone charged with reckless driving has a vehicular manslaughter conviction on their record, that would most likely be considered relevant, as it proves the driver has previously been careless behind the wheel. This information could also be relevant in terms of sentencing, as it would be considered a prior conviction. The driver’s defense lawyer could still challenge this evidence, arguing that it would mislead the jury by drawing them away from the question of whether the defendant drove recklessly.
Evidence can also be ruled irrelevant if it is unfairly prejudicial. For example, if the prosecution tried to introduce photos of dead car crash victims as evidence to illustrate the dangers associated with reckless driving, it would be unfairly prejudicial to the defendant because it only serves to upset the jury without addressing whether or not the accused actually broke the law.
Relevance can also be questioned if the evidence is considered a waste of time. For example, while one character witness may help establish that the defendant is honest and reliable, a dozen would be irrelevant as they would waste the court’s time without providing additional relevant information.
Fighting Evidence Based on Relevancy
While all types of evidence can be fought based on relevancy, the most significant point of contention occurs when the evidence against a defendant is based on past crimes. In sex assault and domestic violence cases, the prosecution will often mention that the defendant has done this before, and a prior conviction is unnecessary. The prosecution just needs victims to testify about the defendant’s previous behavior.
The defense can also use this same tactic to question the victim’s character, showing they aren’t trustworthy, have something to gain through the allegations, or have a propensity for violence.
For example, if an alleged victim says she was assaulted and there are no witnesses to back up her story, it might not be relevant to point out that she has been in a similar situation in the past. But if she has claimed to have been assaulted a dozen times in the past and has never had a single witnesses support her claims, the defense might be able to argue that this shows she has a propensity for making false allegations and could be making up her story for one reason or another.
What Makes Evidence Unreliable?
In terms of admissibility, reliability is most commonly questioned during witness testimonies, however, it can also apply when it is impossible to prove the origin of a physical piece of evidence. For example, while someone’s diary can be used as evidence, it would be inadmissible if you can’t prove it belonged to that person.
Reliability can also be an issue if the chain of custody cannot be traced from the time the police discover a piece of evidence to the time it appears in court, as even a short disappearance means the evidence could have been tampered with at some point.
Hearsay is the most well-known type of unreliable evidence. It involves a witness testifying that they heard someone say something, rather than actually having the person who made the statement testify in court. There are many exceptions to hearsay though, including when someone makes a dying declaration. Because the rules regarding reliability, particularly hearsay, are so complicated, always ask your lawyer if you have any questions regarding whether or not evidence may be considered reliable.
The Admissibility of Illegally-Obtained Evidence
The United States Constitution protects citizens from unreasonable search and seizure, but sometimes officers still neglect to follow proper procedure and collect evidence illegally. When this happens, your defense attorney can challenge anything uncovered through a warrantless search so it cannot be used against you.
Similarly, if you confessed under duress or your rights were otherwise violated in getting you to admit your guilt, your attorney may ensure your statements are withheld from trial.
If I Wasn’t Read my Miranda Rights, is What I Said Inadmissible?
Miranda warnings only have to be read if a suspect is under arrest and questioned. If the police do not question you after arrest, they do not need to Mirandize you. During the investigation, the police can ask you questions without a Miranda warning if you are free to leave.
The evidence admitted into a trial can make or break a case. If enough evidence is inadmissible, the charges can sometimes be dropped altogether. You must work with a top attorney who can ensure that evidence that benefits you is admissible, while that which does not is excluded from the trial. If you have been charged with a crime, Peter M. Liss can help you fight the charges by challenging any questionable evidence. Please call (760) 643-4050 to schedule a free initial consultation.
