In court a trial is held to determine specific facts and the legal implications of those facts. In a criminal trial, the question is if the defendant broke a law and should suffer penalties from a fine to a prison term. In a civil trial, the question is if the plaintiff was harmed by the defendant and should pay the defendant damages.
These questions are decided by presenting evidence to a “fact finder”. In some situations this may be a judge. In other situations it may be a jury. Evidence is presented to the fact finder by the testimony of witnesses. The witnesses describe either their version of events, relate other relevant information, or identify physical evidence to assist the fact finder in determining a criminal defendant’s guilt or a civil defendant’s liability.
Direct evidence is based on a witness’s personal knowledge or observation of a fact. If the witness personally saw the defendant stab the victim that is direct evidence; the stabbing is within the witness’s actual experience. Whether the judge or jury, whose duty is to listen to the evidence and determine the truth, believes the witness is a separate issue regarding credibility, but does not change the nature of the testimony as direct evidence.
Direct evidence has traditionally been described as eye witness testimony. In the modern age photographs, video and audio recordings are also direct evidence. The recorded presentation of an event can establish directly that the event took place.
Circumstantial evidence is more complex. A witness did not see the stabbing above. The witness did see the defendant go into the house carrying a knife. The witness heard a scream inside the house and saw the defendant run out, not carrying the knife. The victim is later found inside with a knife in her back. A reasonable inference is that the defendant stabbed the victim. Whether that fact is true will determine if the defendant is guilty.
Circumstantial evidence is direct evidence of a fact which reasonably infers the existence or nonexistence of another fact. Circumstantial evidence is not direct observation of a fact that is in dispute. In the stabbing above, no one saw the victim stabbed, and the defendant said he did not do it, but the eye witness saw things that lead to the conclusion that the man running out of the house stabbed the victim. The witness’ testimony is circumstantial evidence of the defendant’s guilt.
Circumstantial evidence is a collection of facts that, when considered together, can be used to infer a conclusion about something unknown. Circumstantial evidence is used to support a theory of a sequence of events. The sum total of multiple pieces of corroborating evidence, each piece being circumstantial alone, build an argument to support how a particular event happened. In civil and criminal investigations, corroboration is often supplied by one or more expert witnesses who provide forensic evidence.
Forensic evidence is developed by the examination of physical items to provide inferences of other facts and to recreate events. In traffic accident cases tire skid marks may be examined to determine a car’s direction and speed prior to a crash. Fingerprints at a scene indicate that a particular person was present. Forensic evidence, presented by expert investigators, is circumstantial evidence since it is presented to establish events that were not observed by the witness.
Circumstantial Evidence in Criminal Law
One of the most important elements of proving a criminal case is the existence in the defendant’s mind of criminal intent, known as mens rea. The fact that a defendant did something does not explain his state of mind. Absent a statement of intent made by the defendant, a defendant’s state of mind must always be proven by circumstantial evidence.
Admissibility of Evidence
Whether evidence an attorney seeks to present at trial is direct or circumstantial, there remains the complex question of if the judge or jury deciding the case will even see or hear the evidence. This is a question of “admissibility”, in essence whether the evidence is reliable. Rules regarding this have developed over hundreds of years and are found in the Federal Rules of Evidence. Most states have built their own rules based upon the Federal Rules. Often information about an event exists, but never gets to a courtroom because in the interests of fairness it has been determined unreliable.
 When a judge acts as the fact finder, this is commonly referred to as a “bench trial”.
 Even recordings or photographs are introduced as evidence through witness testimony. The “fact finder” will not see a picture, view a video or listen to a recording unless there is a witness to testify about the source of the recording and its authenticity.
This sounds a bit confusing. In the hypothetical situation of the stabbing, the witness did directly see the defendant go in and out of the house. The witness personally heard the scream. The testimony regarding the defendant’s entry and exit and the scream are direct evidence of those facts. To the extent they are related to the conclusion that the defendant did the stabbing, they are relevant and circumstantial.