Circumstantial evidence is evidence that relies on an inference to connect it to a conclusion of fact—like a fingerprint at the scene of a crime. By contrast, direct evidence supports the truth of an assertion directly—i.e., without need for any additional evidence or inference.
The so-called “CSI effect” has made juries think there is no case unless the cops found DNA, fingerprints, hair or fiber evidence, etc. So a defense lawyer or other interested person might say, “This is weak case, they got no physical evidence, no DNA, no fingerprints, no fiber or hair evidence, nothing to show my client was anywhere near that store on that night. It’s purely a circumstantial case.”
Well, maybe it’s only on TV and in movies where you hear that. I hope so because, using the standard definition of circumstantial evidence stated above, DNA, finger prints, hair and fiber evidence is all circumstantial evidence. DNA on the grip of a gun [“Touch DNA”] proves that a person touched that gun at some time. [Maybe it doesn’t even prove that.] If other evidence shows that this is the gun used in the crime, the DNA evidence becomes stronger but still doesn’t prove conclusively beyond a reasonable doubt that the owner of the DNA was the shooter. Next would be proof that this person still had the gun in his possession shortly after the shooting, maybe that’s how the cops first found the gun. But what if they found it in a trash can? What if the person whose DNA was on the grip claims it was stolen before the crime? Lots of people fail to report stolen guns, especially if they were legally prohibited from having the gun in the first place.
If the gun had been left at the crime scene [only the Mafia leaves guns at the crime scene because they use guns that are not traceable to them and don’t want to be caught with that gun while escaping the scene] still more evidence is needed to place the owner of the DNA at the crime scene at the time of the shooting. The problem with relying on the DNA evidence alone is that the gun could have been stolen or lost and someone else may have been holding it at the time of the shooting. If this possibilty isn’t answer with other evidence a jury might find that guilt has not beeen proved beyond a reasonable doubt. The DNA only creates an inference until other evidence leads it to the conclusion of an ultimate fact in the case.
Therefore, it is only circumstantial evidence, although a jury might still convict on that alone. Most cases of guilt on circumstantial evidence are won by the prosecution even when there is no direct evidence proving guilt because the circumstantial evidence is abundant, there is just so much of it that while it may leave some doubt, it doesn’t leave any reasonable doubt. Even if not every last dot is connected a jury can find that enough dots are connected. It’s just common sense that when too many coincidences are shown there really is no coincidence at all.
The link above is to a story in Scientific American that discusses cases where Touch DNA was transferred to a crime victim by someone who had previous contact with someone not involved in the crime and who also had reason to have touched the body of the crime victim, an EMT for instance. This is the paradox of advancing technology. As the technology becomes more sophisticated it also become more prone to error.
Most murder cases are proven with circumstantial evidence because killers tend not to commit murder in front of witnesses. Even when there is an eye witness the circumstantial evidence that ultimately proves guilt may be more compelling than direct evidence of eye witnesses, especially if the eye witness was not formerly acquainted with the accused person and recognized him. Eye witness testimony of sudden short events is direct evidence, and is also notoriously unreliable.
The phrase “all they have is circumstantial evidence” is ignorant but remains a popluar phrase and will continue to be heard often. The correct phrase should be, “All they need is enough circumstantial evidence so that taken all together it proves guilt beyond a reasonable doubt.”