Case File 294 · Investigation Psychology

What Does It Mean to Challenge Evidence?

By Murder Book Editorial TeamPublished by Gungrounds, the studio making Murder BookPublished 3 October 2026Updated 3 October 2026

Challenging evidence means formally questioning whether a piece of evidence should be admitted at trial, or disputing its reliability and weight once it is before the court. In criminal cases, the defence can challenge evidence on several grounds: it was obtained illegally, it is unreliable, its handling was flawed, or the methods used to produce it do not meet accepted scientific standards. Challenging evidence is not the same as proving it false. It is a procedural and legal process that asks the court to scrutinise how evidence was gathered, preserved and interpreted before it is used to determine guilt or innocence.

Key takeaways

Challenging evidence means questioning its admissibility, reliability or weight in court.
Common grounds include illegal collection, broken chain of custody, unreliable forensic methods and witness credibility issues.
The exclusionary rule, established in Mapp v. Ohio (1961), bars evidence obtained through unconstitutional searches from being used at trial.
The Daubert standard gives judges a framework for evaluating the reliability of expert and scientific testimony.
Challenging evidence protects due process; it does not necessarily mean the evidence is wrong.

What are the main ways evidence can be challenged?

Evidence can be challenged before trial through pre-trial motions, during trial through cross-examination and objections, or after conviction through appeals. The most common grounds include:

Was the evidence obtained legally?

The Fourth Amendment to the U.S. Constitution protects against unreasonable searches and seizures. If police collect evidence without a valid warrant or an applicable exception, the defence can file a motion to suppress it. The exclusionary rule, applied to state courts through the Supreme Court's decision in Mapp v. Ohio (1961), holds that evidence obtained in violation of the Fourth Amendment is inadmissible.

The related "fruit of the poisonous tree" doctrine, rooted in Silverthorne Lumber Co. v. United States (1920), extends this principle: evidence discovered as a result of an initial illegal search may also be excluded. For example, if an illegal search of a home uncovers a key that leads to a storage unit containing further evidence, both the key and the storage unit contents could be challenged.

There are exceptions. Courts have recognised that evidence may still be admissible if it would have been inevitably discovered through lawful means, if it was found through an independent source, or if the connection between the illegality and the evidence is sufficiently attenuated, as the Supreme Court discussed in Wong Sun v. United States (1963).

Is the chain of custody intact?

Physical evidence must be tracked from the moment it is collected to when it is presented in court. If there are gaps in documentation, missing signatures, unsecured storage or unexplained changes in the evidence's condition, the defence can argue that it may have been contaminated, altered or tampered with. A broken chain of custody does not mean the evidence was tampered with, but it raises doubt about its integrity.

Does the forensic method meet scientific standards?

Expert testimony and forensic evidence can be challenged under the Daubert standard, established by Daubert v. Merrell Dow Pharmaceuticals (1993). Under Daubert, a judge acts as a gatekeeper, evaluating whether the expert's methodology is testable, has been peer-reviewed, has a known error rate and is generally accepted in the relevant scientific community.

This matters because not all forensic techniques are equally reliable. Research has shown that some widely used methods, such as bite mark analysis and certain types of pattern matching, lack the scientific validation that DNA analysis has. The 2009 National Academy of Sciences report on forensic science found significant problems with the scientific foundations of several forensic disciplines.

Is the witness credible?

Witness testimony can be challenged through cross-examination. Defence attorneys may highlight inconsistencies between a witness's current testimony and previous statements, expose potential biases or motives to lie, or question the conditions under which an identification was made. Eyewitness testimony reliability research shows that confident witnesses can still be wrong, making credibility challenges an important safeguard.

What is a motion to suppress?

A motion to suppress is a formal request asking the court to exclude specific evidence from trial. It is typically filed before the trial begins. If granted, the prosecution cannot present that evidence to the jury. Common bases for suppression include:

Evidence obtained without a warrant or probable cause
Statements taken in violation of the suspect's rights
Identification procedures that were unduly suggestive
Evidence whose prejudicial effect substantially outweighs its probative value

Does challenging evidence mean it is wrong?

Not necessarily. A successful challenge means the evidence does not meet the legal requirements for admission or that its reliability is in doubt. The underlying facts may still be true. For instance, evidence that was obtained through an illegal search may be entirely accurate, but the exclusionary rule bars it to deter unconstitutional police conduct.

This distinction is important. The rules governing evidence admissibility exist to ensure that the process of determining guilt is fair, not just that the outcome is correct. A conviction based on improperly obtained or unreliable evidence undermines the integrity of the justice system even if the defendant is factually guilty.

What is the role of expert witnesses in evidence challenges?

Expert witnesses play a significant role on both sides. The prosecution may call forensic experts to explain DNA matches, toxicology results or digital evidence. The defence may call its own experts to challenge the methods used, highlight limitations or offer alternative interpretations.

Under the Daubert standard, both sides' experts are subject to the same reliability test. A judge can exclude expert testimony from either party if the methodology does not meet the required threshold. This gatekeeping function is especially important in cases involving newer or less established forensic techniques, where the scientific community may not have reached consensus on reliability.

The 2009 National Academy of Sciences report recommended significant reforms to forensic science practices in the United States, including the development of standardised terminology, proficiency testing and independent oversight. These recommendations reflected concerns that some forensic disciplines had been admitted in court without adequate scientific validation.

Why should investigators care about challengeable evidence?

Investigators who understand how evidence can be challenged are better positioned to collect evidence that will withstand scrutiny. This means following proper procedures for searches, documenting the chain of custody carefully, using validated forensic methods and conducting fair lineups. Evidence that is collected properly is harder to challenge and more likely to serve its purpose at trial, whether that purpose is to support a conviction or to exonerate a suspect.

How does Murder Book let players question what they find?

Murder Book: The Art of Interrogation is an upcoming narrative interrogation game from Gungrounds, an independent studio in Zagreb, Croatia. Players examine suspect statements and behavioural cues, but the game does not tell you which pieces are reliable. Development screenshots show an in-game casebook listing behaviours such as Fabrication, Avoidance and Narrative Gaps. The evidence board links statements that may contradict each other, and players must decide what those contradictions mean.

The game's structure asks players to do something similar to challenging evidence: look at what you have been given, question whether it is trustworthy and consider whether the story holds together. Cases are designed for focused 5–10-minute sessions.

Murder Book is in development for PC (Steam) and mobile, with release currently planned for the end of Q2 2027.