Criminal evidence is often considered direct or circumstantial. Direct evidence demonstrates proof beyond a reasonable doubt that an individual committed a crime, while circumstantial is based on theory or implies truth to an allegation but does not prove it. Circumstantial and direct evidence may come in many forms including: testimony, documentary, physical, digital, exculpatory, scientific, and genetic.

Testimony

This type of evidence is obtained from a witness who makes a statement. It may be oral or written and is usually made under oath. Opinions or inferences in testimony are typically limited to expert witnesses. Opposing attorneys can object when a witness is asked a question. This legal maneuver is an attempt to disallow what the objecting side deems an improper question. When objecting, a lawyer needs to give a standard reason why, such as "argumentative," "call for speculation," "hearsay" or "irrelevant'.

Physical

Physical evidence is just that, a piece of evidence presented to prove a fact based on its physical characteristics. It can include part or all of an object. This can range from DNA, to a weapon, a document or piece of furniture that has evidence attached.

Documentary

Evidence presented at a trial in document form is called documentary evidence. The assumption is this evidence is just writing on paper, but it can include any form of media. Photographs, video and audio all count as documentary evidence. At times, what appears to be documentary evidence is actually physical evidence. For example, if a letter covered in blood is entered as evidence, the blood is the focus of the piece of evidence and hence the paper will be entered into trial as physical evidence.

Digital

This is evidence stored or provided in digital form to be used at trial. The use of this kind of evidence has increased as the use of technology has increased. E-mails, ATM transaction logs, digital photos, spreadsheets, Internet browser histories, just about anything with an electronic history can be used as digital evidence.

Exculpatory

This tends to clear the guilt of the defendant at trial. Police and prosecutors in the United States must disclose any exculpatory evidence to the defendant or risk a dismissal of the hearing. For example, A person is arrested for a murder because they are found running away from a crime scene however an eyewitness testifies that another person actually committed the murder. The witness’ testimony is exculpatory evidence.

Scientific

Crime scene analysis combines the human intelligence with scientific procedures and methods to interpret what has occurred. While the scientific evidence may speak for itself, it is often supplemented by expert witness testimony. All states have rules on expert testimony and scientific evidence.

Eyewitness

An eyewitness is someone who witnesses a crime or wrongdoing by seeing it firsthand. There are problems with this type of evidence. It is the leading cause of wrongful conviction in the United States. According to the Innocence Project, "Eyewitness misidentification is the single greatest cause of wrongful convictions nationwide, playing a role in more than 75% of convictions overturned through DNA testing."

Genetic

DNA profiling/testing is used to help identify an individual who is responsible for a crime. State laws on the use of genetic testing in the United States vary. Genetic evidence can be collected without the suspects' knowledge.