In a criminal case, evidence is inadmissible if authorities obtained it illegally or if it’s inadmissible evidence according to that state’s judicial rules. If evidence is inadmissible, prosecutors are hard-pressed to prove their cases. Prosecutors must establish guilt beyond any reasonable doubt. So, they need all the evidence they can get.
What is Admissible Evidence?
Admissible evidence in a criminal case usually includes testimonial, scientific, and electronic evidence. A DUI-collision case illustrates all three kinds of evidence.
An eyewitness testifies that the defendant was driving the car at the time of the wreck. A Breathalyzer test, or more likely a blood test, “testifies” that the defendant was intoxicated. Electronic evidence, usually surveillance camera footage, shows how the wreck happened.
Scientific and electronic evidence are only admissible if an expert witness authenticates the “testifying” device or method (e.g. collecting a blood sample). More on that below.
Evidence, not opinions or speculation, is the foundation of a criminal court verdict. Judges and jurors weren’t there and didn’t see what happened. Therefore, they rely on evidence to make accurate judgments. Appeals courts routinely throw out convictions based on inadmissible evidence.
What Makes Evidence Admissible?
Evidence is inadmissible unless it complies with all procedural (evidence collection) and substantive (reliability) requirements.
Key procedural requirements include the rights guaranteed in the Fourth, Fifth, Sixth, and Eighth Amendments.
Under the Fourth Amendment, physical evidence is inadmissible unless officers had a valid search warrant or a search warrant exception applied.
Judges may only issue search warrants if officers present probable cause affidavits. An affidavit is a physical, written document, not a phone call, text message, or email attachment. Probable cause could be an issue if officers over-relied on paid informant testimony. Most snitches receive cash or leniency in exchange for their testimony. Many people will say practically anything for love or money.
Over the years, courts have carved out some exceptions that make otherwise inadmissible evidence admissible in court. Owner consent might be the most common exception. An owner, or an apparent owner (e.g. a driver who doesn’t legally own the vehicle) may voluntarily consent to a search.
“Voluntary” is the key word. Courts usually allow officers to bully or threaten people to obtain consent, at least somewhat. However, at some point, bullying and threatening crosses the line and renders consent involuntary.
Incidentally, some officers tell people they’ll get warrants if they don’t consent to a search. That’s an empty threat. If officers had probable cause to obtain a warrant, they wouldn’t ask for consent.
Fifth Amendment violations are common as well. Most people are familiar with the Miranda Rights (you have the right to remain silent, etc.), These rights apply much earlier, and are much broader, than most people believe.
Only reading defendants their rights legally paves the way for custodial interrogation. In this context, “custody” means the defendant doesn’t feel free to leave. Most people don’t feel free to leave when officers turn on overhead squadcar lights.
The Fifth Amendment applies to actions as well as spoken words. Defendants may refuse to appear in lineups, pose for pictures, and handle evidence. Defendants must only obey basic “step out of the car” commands.
The Sixth Amendment guarantees the right to counsel. The Eighth Amendment guarantees reasonable bail in criminal cases. An unrepresented defendant taking on prosecutors is like a pee-wee football team taking on an NFL team. Pretrial detention hamstrings a criminal defense.
There’s more. Legally obtained evidence is inadmissible in court unless the judge rules the evidence is:
- Relevant: Evidence is relevant if it makes a material fact more or less probable, and the proof isn’t unfairly prejudicial. Let’s go back to the DUI-collision example. The defendant’s bad driving record isn’t relevant. Good drivers cause crashes too. Furthermore, the bad driving record is unfairly prejudicial. Jurors might punish the defendant for being a bad person instead of causing that collision.
- Reliable: Most CSI-type scientific evidence, like clothing fibers and footprints, is unreliable. These kinds of evidence are more science fiction than science fact. Significantly, there’s a difference between reliable and accurate. A broken clock is accurate twice a day.
- Credible: This area is closely related to reliability. Witnesses are unreliable if they’re not credible. If Lisa says Tom assaulted her and the two are involved in a divorce case, her testimony is unreliable. Once again, it may be accurate, but there’s a difference between accurate and credible.
An expert witness must authenticate physical evidence. The blood test in the aforementioned DUI-collision case is only admissible if doctors took the sample correctly and it was stored correctly.
The expert must also be credible. Usually, jurors decide if a witness is credible. If a police technician testifies that a Breathalyzer was working properly and a defense expert testifies that the gadget wasn’t working correctly, jurors decide who is more reliable.
Sometimes, these two areas overlap. Hearsay is a good example. Assume Bill witnessed a bank robbery. He told Tony what happened. Tony cannot testify in court because his testimony is hearsay. He only knows what Bill told him.
Flawed lineups are another example. Double-blind lineups (neither the administering officer nor the witness know the suspect’s identity) are much more reliable than single-blind lineups. Officers usually give witnesses clues, like placing the suspect in the middle of the line or asking “Are you sure it’s Number Five? You don’t think it’s Number Four?”
On a related note, lineup instructions are important as well. Usually, witnesses feel like they must pick someone, even if they’re unsure of the suspect’s identity. Officers lift this burden if they say the suspect “might or might not” be in a lineup.
Possible Consequences of Inadmissible Evidence
As mentioned, prosecutors must meet a very high burden of proof in criminal cases. So, if the judge rules that evidence is inadmissible, that ruling effectively derails the prosecutor’s case.
Usually, the judge decides if evidence is inadmissible after a pretrial hearing. Assume Phil is charged with DUI and the judge rules the Breathalyzer wasn’t properly calibrated. Prosecutors must then move forward with circumstantial evidence, usually the results of the one-leg stand and other field sobriety tests. The conviction rate in circumstantial evidence DUIs is much lower than the conviction rate in chemical test DUIs.
As a side note, this issue is very common. The Massachusetts Supreme Court recently threw out 27,000 DUI convictions for this very reason.
So, inadmissible evidence usually forces prosecutors to offer favorable plea bargain deals. That offer might be a plea to a lesser-included offense. In some jurisdictions, prosecutors often reduce weak-evidence DUIs to reckless driving. This offense, while it’s a serious crime, doesn’t have the same collateral consequences as DUI.
If the judge rules evidence is inadmissible at trial, the consequences could be even worse. Prosecutors not only lose the evidence. They also lose credibility with jurors.