Criminal prosecutors use a number of methods, including eyewitness identification and testimony, written or verbal confessions and jailhouse informants, to form cases and attempt to convict suspects of committing a crime. One commonly used method is forensic testing of evidence found at the crime scene. According to the Innocence Project, errors and mistakes involving forensic testing were involved in more than 45% of wrongful conviction cases. These are cases in which suspects were exonerated after DNA evidence proved their innocence.
Sadly, errors made during testing processes, as well as misapplication of the test results, can lead to the wrongful conviction of innocent people. In some cases, defendants were convicted of a crime only to find out decades later that a mistake was made with forensic tests used in the case. Some tests have not been scientifically proven to yield accurate results, while others are outdated or no longer used at all. These tests include the following:
- Methods used to detect a fire’s point of origin
- Hair follicle comparisons
- Comparing the lead in a bullet found at the scene to bullets possessed by the suspect
Expert witnesses may inadvertently or intentionally mislead the jury when revealing critical test results in their testimony. Technicians that are unskilled, untrained or wish to alter the results, may manipulate scientifically proven methods, such as DNA profile testing. Studies show that DNA profiles may also match with more than one person.