Circumstantial evidence is evidence that relies on an inference to connect it to a conclusion of fact—such as 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. Overview On its own, circumstantial evidence allows for more than one explanation. Different pieces of circumstantial evidence may be required, so that each corroborates the conclusions drawn from the others. Together, they may more strongly support one particular inference over another. An explanation involving circumstantial evidence becomes more likely once alternative explanations have been ruled out. Circumstantial evidence allows a trier of fact to infer that a fact exists. In criminal law, the inference is made by the trier of fact to support the truth of an assertion (of guilt or absence of guilt). Reasonable doubt is tied into circumstantial evidence as that evidence relies on inference. It was put in place because the circumstantial evidence may not be enough to convict someone fairly. Reasonable doubt is described as the highest standard of proof used in court and means that a juror can find the defendant guilty of the crime to a moral certainty. Even when circumstantial evidence is not sufficient to convict or acquit, it can contribute to other decisions made about the case. Testimony can be direct evidence or it can be circumstantial. For example, a witness saying that she saw a defendant stab a victim is providing direct evidence. By contrast, a witness saying that she saw a defendant enter a house, heard screaming, and saw the defendant leave with a bloody knife is circumstantial evidence. It is the need for inference, and not the obviousness of the fact inferred, that determines whether evidence is circumstantial. Forensic evidence supplied by an expert witness is usually treated as circumstantial evidence. For example, a forensic scientist or forensic engineer may provide results of tests indicating that bullets were fired from a defendant's gun, or that a car was traveling over the speed limit, but not necessarily that the defendant fired the gun or was driving the car. Circumstantial evidence is especially important when there is little or no direct evidence. Civil law Circumstantial evidence is used in civil courts to establish or refute liability. It is usually the most common form of evidence, for example in product liability cases and road traffic accidents. Forensic