Latent prints found on more porous surfaces are treated with chemicals that reveal print patterns by reacting with some component of the print residue. The reaction creates another compound that is more clearly visible. Common used for expossing prints include: cyanoacrylate vapor, iodine fuming, ninhydrin, and silver nitrate.

Cyanoacrylate Vapor

What is cyanoacrylate? You probably know it by it’s trade name, Super Glue. Yes that super glue, the kind you can buy in virtually any hardware or hobby store. It turns out super glue is 98 percent cyanoacrylate, which has become an extremely useful forensic tool. When heated or mixed with sodium hydroxide, cyanoacrylate releases vapors that blind to amino acids that are present in print residues, thus forming a white latent print.

After a print has been exposed with cyanoacrylate, it can be photographed as is or be treated with a flouresent dye that binds to the print. The print then glows under a laser or ultraviolet light.

The item that is to be checked for prints in this manner often is exposed to the vapor in somthing called a fuming chamber. The rsulting fumed print is quite hard and stable, as you’d probably expect from Super Glue.

Iodine Fuming

When heated, solid crystal iodine realeases iodine vapors into a fuming chamber, where iodine fumes combine with oils in the latent print to produce a brownish print. This kind of method fade quickly, so it must be photographed right away or fixed by spraying it with a solution of starch in water, which preserves the print for several weeks or months.

By tomorrow I’ll write about ninhydrin and silver nitrate.

- Brandon Anderson

Time of Death seems like a simple and strait forward concept - it’s the exact time that the victim drew his or her last breath, right? Wrong. Time of deaths may actually come in three different forms:

Estimated: The best guess as determined by the ME.
Legal: The time when the body was discovered or pronounced dead. The legal time is also the time printed on the death certificate.
Physiological: The time at which the victim’s vital functions actually ceased.

Times of death may differ by days, weeks, even months, if the body isn’t found until well after physiological death has occurred.. For example, if a serial killer kills a victim in July, but the body isn’t discovered until October, the physiological death took place in July , but the legal death is in October. The ME’s estimated time of death could be in July or even June or August.

The only absolutely accurate determination of the death is under the uncommon circumstances in which a person dies with a physician or other skilled medical professional present. many deaths occur during sleep, and accidental  deaths often occur when the victim is alone, and so do suicidal deaths. In homicides, the perpetrator typically is the only witness, and even if he checks his watch, he’s not likely to pass on that information.

- Brandon Anderson

There are alot of tools and equipment used by Crime Scene Investagators so ill list the most common tools and equipment used by Crime Scene Investagators,

• Crime Scene tape to cordon off the area
• A flashlight
• Latex gloves and paper shoe covers
• A magnifying glass and tweezers for collecting trace evidence
• A pen, logbook, and sketchpad
• Measuring tapes and rulers
• A camera with black and white and color film and several different lenses
• An assortment of paper, plastic, and glass containers store collected materials
• Sealable evidence bags
• Portable alternative light sources - laser, ultraviolet, and infrared
• Basic fingerprint kit with powders and lifting tape
• Casting kit for three-dimensional shoe and tire impressions
• Gunshot residue detection kit
• Chemicals to locate occult bloodstains
• Serology kit for sampling blood and other biological fluids
• Rape Kit

- Brandon Anderson

The technique of “stringing” — attaching strings to each spatter to see where they converge — is just one way to determine the area of convergence, or source of the blood. Most TV shows, like “Dexter,” focus only on the analyst looking at the strings and making statements about the crime, not on the process involved. In the stringing method, which is still used by many analysts, the analyst documents the location of each spatter using the coordinate system. Then, he or she establishes a level line to show how the spatter is oriented in relation to the floor and ceiling.

Using elastic string, the analyst draws lines from each spatter through the level line. Then, he or she uses a protractor on the level line in the area where the strings converge to determine the angle of flight for each spatter. If the spatters are mostly on a wall, the analyst can measure the distance from the area of convergence to the wall to find out where the victim was located.

Some analysts use trigonometric calculations to find the area of convergence, which basically means that they use triangles to figure it out. The measurements of the blood stain become the sides of a right triangle. The length of the stain is the triangle’s hypotenuse, and its width is the side opposite the angle the analyst is trying to find.

First, the analyst has to locate each spatter and measure its length and width using a scale, a ruler or calipers. Then, he or she computes the angle using this formula:

angle of impact = arcsin (opposite side/hypotenuse)

Here’s what an analyst has to do to for this to work:

1. Measure the length and width of the splatter.
2. Divide the width of the splatter by its length.
3. Determine the arcsin of that number, typically using a calculator with an arcsin function.

A drop of blood that fell perfectly vertically, or at a 90-degree angle, will be round. As the angle of impact increases, the drop of blood gets longer and develops a “tail.” This tail points in the direction that the drop traveled, but its length isn’t part of the measurements.

The greater the difference between the width and length, the sharper the angle of impact. For example, imagine a bloodstain 2 millimeters wide and 4 millimeters long. The width divided by the length is 0.5. The arcsin of 0.5 is 30 — so the blood hit the surface at a 30-degree angle. In a bloodstain that is 1 millimeter wide and 4 millimeters long, the ratio between them is 0.25. In this case, the blood hit the surface at about a 14-degree angle.

A third method involves taking the length and width of each blood spatter as well as other measurements of the area and putting them into a computer program, such as No More Strings. These programs create three-dimensional models and animations of the crime scene and show the area of convergence. When used to present evidence, computer programs can be more compelling and convincing than jargon-filled expert testimony or two-dimensional photographs.

Bloodstain pattern analysis (BPA) is one of several specialties in the field of forensic science. The use of bloodstains as evidence is not new, however the application of modern science has brought it to a higher level. New technologies, especially advances in DNA analysis, are available for detectives and criminologists to use in solving crimes and apprehending offenders.

The science of bloodstain pattern analysis applies scientific knowledge from other fields to solve practical problems. Bloodstain pattern analysis draws on biology, chemistry, maths, and physics among scientific disciplines. As long as an analyst follows a scientific process, this applied science can produce strong, solid evidence, making it an effective tool for investigators.

For more information on bloodstain analysis and blood spatter alalysis I reccomend you take a look at these two older posts,

Blood Spatter Catagories

and

Blood Spatter Catagories Continued

- Brandon Anderson