Blood Stains & Analysis

In any violent crime, there is bound to be blood. Whether it is from a stabbing, a gunshot, or being beaten to death, blood is bound to be present at the crime scene.

BPA (blood pattern analysis) is used a crime scene to “recreate the actions that caused the bloodshed” (“A Simplified Guide”). Analyzers use a number of clues (shape, size, distribution, location) to help them determine the things that occurred or did not occur.

A wall surface with a small splash of fake blood dripping downward

In the image above, blood has been spattered on the wall. Examiners can look at this pattern to determine where the person it came from was located when they were hit.

 

BPA uses biology, physics, and mathematics to answer the questions investigators ask when blood is present at a scene. These questions include:

  • “Where did the blood come from?”
  • “What caused the wounds?”
  • “From what direction was the victim wounded?”
  • “How were the victim(s) and perpetrator(s) positioned?”
  • “What movements were made after the bloodshed?”
  • “How many potential perpetrators were present?”
  • “Does the bloodstain evidence support or refute witness statements?”

Even though the patterns of blood may seem completely random and impossible to decipher a story of what happened from, highly trained blood analyzers know how to examine the blood to figure out what happened. Analyzers look at spatters, transfers, and voids to determine what happened. The lack of blood can be just as telling as the presence of blood. Angle of the blood spatter, how dry it is, and the shapes or prints left in the blood can help investigators determine what happened at the scene of crime. This is why blood analysis is very important – it can prove or disprove what happened at a crime and can also determine who was or was not involved in the crime. It is important to proving guilt as well as innocence.

Source: “A Simplified Guide To Bloodstain Pattern Analysis.” Forensic Science Simplified. 2013. Web. 9 Dec. 2015.

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Fingerprinting Part 2

So, continuing off the last post about fingerprinting and the types and how those are collected, there is also the process of analyzing them and part of that is the people who do it.

These people are called fingerprint examiners or analyzers. They are usually trained and certified to be able to examine the fingerprints. Fingerprint examiners look at the fingerprint with a type of microscope called a loupe and they use a tool called a ridge counter to “count the fraction ridges” (“A Simplified Guide”). These examiners ultimately decide if a print is useful enough to be compared (using a computer system) to other known prints to see if the owner of the print can be found.

The image below is of a fingerprint examiner using a loupe to analyze prints. lp3-3-10-28-11-003

Fingerprint examiners use what is known as the ACE-V method to examine a fingerprint. This stands for analysis, comparisons, evaluation, verification.

During the analysis portion, the print is examined to determine if it is necessary to even move on to the next stages of the ACE-V method. The quality may not be sufficient or there may not be enough of the print to be useful for a comparison. If the print is deemed usable, the characteristics that will be used in a comparison are determined. In addition, the analysis can “uncover physical details such as recurves, deltas, creases and scars that help indicate where to begin the comparison” (“A Simplified Guide”).

In the comparison part, a fingerprint examiner will look at the “known and suspect prints side-by-side.” The examiner looks at the tiniest details of the prints and the locations of those details to decide if they are a match. The next step is evaluation, where the examiner will make the call on “if the prints are from the same source” or different sources, or the examiner will decide that the results are inconclusive (“A Simplified Guide”).

The last step, verification, is when another examiner goes through the process described above with the same print to “either support or refute the conclusions” of the first analysis.

Because of the uniqueness of fingerprints, they can be used as a form of identification. No two people have the same fingerprint, as demonstrated by the FBI’s Integrated Automatic Fingerprint Identification System (IAFIS), which contains over 72 million fingerprints from various sources. Just about every time something is touched, a fingerprint is left behind, along with the identity of the owner of that print.

Source (for this post and the previous one): “A Simplified Guide To Fingerprint Analysis.”Forensic Science Simplified. 2012. Web. 4 December 2015.

Fingerprinting

Fingerprints are an important part of a criminal investigation. Every person has a unique fingerprint, and there are different ways of collecting them from certain types of surfaces.

Almost any surface can hold a fingerprint when it is touched. People who study fingerprints are called fingerprint analyzers and they classify fingerprints into three categories: three-dimensional plastic, patent, and latent. Three-dimensional plastic prints are found “on soft surfaces [such as] soap, wax, wet paint, fresh caulk, etc” (“A Simplified Guide”).  Patent prints are visible and latent prints are invisible.

Since patent prints are visible, most of them can simply be photographed. If better visibility is needed, powder and dyes can be applied to improve the quality of the print.

For latent prints, fingerprint powder can be applied and the powder will stick to the print. It can then be photographed. The print is sometimes lifted from the surface with clear tape and applied to a piece of paper to preserve it. The cyanoacrylate method can be used on latent prints as well. The object the fingerprint is on will be placed in a chamber and vapors from superglue are put in the chamber. These vapors will adhere to the print and it is then visible. Chemicals can be used as well as certain compounds attach to the residue of a latent fingerprint. A chemical called ninhydren will cause the print to turn purple, which makes it easier to photograph.

Fingerprints are left on surfaces almost any time it is touched. This makes collecting and analyzing these prints an important part of any investigation. If correctly identifying, a carelessly left print can lead investigators back to the perpetrator of the crime and help bring him or her to justice.

Source: Listed on Fingerprinting Part 2