Scientific and Forensic Evidence

Scientific evidence and forensic science establish facts through science. For example, DNA evidence can help establish the identity of persons at a crime scene. A forensic scientist has the expertise to develop and apply DNA evidence.

Scientific and forensic evidence are two types of opinion evidence used during a criminal trial. Expert witnesses offer an opinion based on their expertise.

For example, a blood splatter analyst can offer an opinion on blood splatter evidence. The expert witness's role is to help the trier of fact (jury or judge) understand the scientific evidence with an expert opinion.

The following provides an overview of scientific and forensic evidence used in criminal trials.

What Is Scientific Evidence?

These types of evidence often reveal hidden clues about a crime or criminal event. Like other types of evidence, scientific and forensic evidence must meet specific rules and standards before a court of law will admit it into evidence.

Determining Admissibility of Scientific Evidence

In Daubert v. Merrell Dow Pharmaceuticals, the U.S. Supreme Court established a framework for the review and admission of scientific evidence.

Under Daubert, the Federal Rules of Evidence provide the standards for admitting scientific evidence in a federal trial. Judges must make a preliminary assessment of the scientific evidence before the jury hears the evidence.

The Supreme Court held as follows:

  • Judges determine if the scientific evidence has enough merit and weight for presentation to the jury
  • Judges determine if the scientific evidence is both relevant and reliable
  • Evidence should have a scientific foundation

The Supreme Court recognized that the judge is the gatekeeper for the jury. They must make an admissibility determination before the jury can review the evidence.

Daubert Motions

If one party wishes to challenge a piece of evidence before the jury sees it, they can file a Daubert motion for an admissibility determination. The judge will hold a hearing before ruling on the admissibility of the scientific evidence. A forensic expert may testify before the judge and explain their methodology. The judge will then decide to either admit or exclude the evidence.

The techniques used to develop forensic evidence are often too advanced for many judges and juries. Expert witnesses help judges understand the forensic evidence.

Forensic Evidence

Forensic evidence is a type of scientific evidence because it relies on the scientific method. The methods used to gather, develop, and analyze these types of evidence are often beyond the scope of knowledge that judges and juries possess, so attorneys rely on expert witnesses to guide the judge and jury through the scientific evidence.

Forensic evidence in criminal cases includes the following pieces of evidence gathered through a criminal investigation:

  • DNA analysis, which includes DNA tests and DNA profiles
  • Fingerprint analysis
  • Tool marks
  • Ballistics analysis
  • Trace evidence
  • Toxicology test results and reports

Forensic scientists use physical evidence discovered by law enforcement and crime scene analysts to develop forensic evidence in a crime laboratory.

For example, a crime scene investigator may recover blood from a crime scene. The forensic scientist can use that blood sample to run a DNA test and compile a DNA profile. They can then use that DNA profile to find potential witnesses or the perpetrator through DNA matching.

Using Scientific and Forensic Evidence

Criminal defense lawyers use scientific and forensic evidence to strengthen their client's case. Often, this evidence can create enough reasonable doubt to get an acquittal of all criminal charges.

But, judges can exclude forensic evidence from a trial if it doesn't meet the criteria laid out in Daubert and the Federal Rules of Evidence (FRE). The reliability of forensic evidence is a critical factor in determining admissibility.

Forensic scientists objectively gather and develop scientific evidence using the scientific method. The scientific method should meet the following criteria:

  • Objective
  • Unbiased
  • Researched in a controlled environment

It is imperative to establish the scientific theory in the scientific community and subject it to rigorous peer review before the trial. Once the scientific community accepts or validates the theory, an attorney may offer it as evidence at a trial.

At one point, fingerprint identification was considered junk science. After decades of use, it is clear that fingerprint identification is a reliable type of forensic evidence. Courts regularly admit fingerprint evidence into evidence.

Attorneys who want to introduce new types of forensic evidence must first convince a judge of its reliability.

Get Legal Help

Although scientific and forensic evidence can help strengthen a case, they are subject to scrutiny. A qualified criminal defense attorney can help. They are experts in criminal law and can challenge a blood sample's chain of custody or the improper calibration of a radar gun.

Many criminal defense attorneys specialize in scientific and forensic evidence and can call expert witnesses in your defense. Speaking to an experienced criminal defense attorney about your case can help protect your rights.

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