What is Gun Shot Residue or (“GSR”)

What is gunshot residue?

Gunshot residue, often abbreviated “GSR”, is a type of forensic evidence. GSR is the substances that come out of a firearm after it is discharged. Pulling the trigger of a firearm causes a small explosion to occur inside the barrel of a gun that makes the bullet project out of it. As this happens, several residues are released. These include primer residue, residue from the projectile itself, and residue from unburnt or partially burnt gunpowder.

What does GSR show in a criminal investigation?

GSR can be analyzed by a forensic scientist to help prove or disprove a case against a person accused of a crime. If discovered on a person’s body, GSR can also help show that a person discharged a firearm. GSR could be used to show that a gun was transferred from one person to another. Since GSR typically lasts for no more than 4-6 hours on a person, it can also be used to help show when a firearm was discharged.

Take for example a case where a person is accused of discharging a firearm within 500 feet from a building. This is a crime in Massachusetts. To convict a person, the government must prove beyond a reasonable doubt that the accused discharged the firearm. Say police respond to a report of a gunshot fired in a residential area. They discover a bullet hole in a wall and arrest a person with a firearm in the trunk of their vehicle. A forensic analysis of the gun and suspect’s clothing could determine that no GSR was present. This would help prove that the gunowner was not the person who discharged the firearm.

Is GSR analysis flawless?
GSR analysis is not perfect and does not always guarantee a person is guilty of a crime. All crimes must be proven beyond a reasonable doubt. This is one of the highest burdens of proof in law. An effective criminal defense lawyer will consult an expert to determine if a finding of GSR was reliable. There are various ways a GSR analysis could not be reliable.

For example, there could be a false positive. GSR might not necessarily come from a firearm. It could come from another explosive device, like a lawfully discharged firework or a piece of machinery. The sample of GSR could also have been contaminated in the lab.

How can GSR evidence be challenged?

There are a variety of ways to challenge GSR analysis. In addition to challenging the scientific reliability of a GSR analysis, the way GSR evidence was collected could be disputed.

For instance, GSR may have been collected in violation of a person’s constitutional rights. The Fourth Amendment of the US Constitution protects people from unreasonable searches and seizures. The burden of proof called probable cause is usually required. If a person were stopped during a traffic stop, police opened the trunk of the car without probable causeor any other lawful justification, and discovered a gun with GSR on it, that evidence most likely would not be allowed into evidence at trial because it was collected illegally by police.

Thanks to modern technology, forensic science has become a much more valuable tool for solving crimes. For example, the development of DNA analysis has given law enforcement the ability to compare DNA left at crime scenes to DNA stored in databases to help them identify suspects. Although DNA comparisons might be the most well-known modern forensic science technique, it is not the only one. Forensic scientists can also examine gunshot residue (GSR).

GSR analysis is a valuable forensic science, but like all techniques used to prove people guilty of crimes, it has its limitations. Recognizing these limitations may be the difference between whether a person is wrongly convicted of a crime or rightfully acquitted.

What is forensic science?

The definition of forensic science is the application of science to law. In criminal law, it includes using scientific techniques to determine if a person is guilty or innocent of a crime. The fields of science that could be involved include:

  • Physics
  • Chemistry
  • Biology
  • Computer science
  • Engineering
  • Data analysis

For example, in a drug case, chemistry might be used to determine whether a substance is an illegal narcotic (for example, cocaine). In a case involving possession of child pornography, data analysis could be performed to document when files were downloaded and opened. Likewise, biology could be used in a murder case to show a victim’s cause of death.

Forensic science is practiced by forensic scientists. Forensic scientists work in forensic crime laboratories. Forensic crime labs receive forensic evidence, analyze it using scientific techniques, and report their findings to law enforcement. Forensic evidence could include:

  • Blood
  • Saliva
  • Hair
  • Semen
  • Soil and vegetation
  • Fingerprints
  • Tire tracks
  • Narcotics
  • Computer files
  • Financial data

Forensic scientists often work for police but not always. For example, Massachusetts has a crime laboratory run by the State Police. Criminal defense lawyers will often use the services of an expert to conduct an independent forensic analysis of evidence. For example, an expert might be used by a criminal defense lawyer to analyze data on financial transactions to determine if the state will be able to prove their client committed a crime like larceny or fraud.

A forensic scientist who provides testimony in a case must be properly qualified. This usually means having degrees or certifications. Their methods must also be scientifically valid and recognized. For example, it is not very likely that a court would allow the testimony of an astrologist who says a person is guilty because of the way the stars were aligned on the night a crime was committed. On the other hand, a MIT PhD with an impressive CV who testifies to the flaws of a ballistics analysis would likely be allowed.

An criminal defense attorney will be very familiar with the law on searches and seizures. It is the job of an effective criminal defense attorney to ensure the constitutional rights of people charged with crimes are protected. This means paying close attention to how evidence was collected and ensuring that it is used fairly at trial.



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