Forensics- Spatter & Glass Analysis

Equation to find the angle of impact of blood splatter

sin^-1(width/length)

characteristics of high velocity blood splatter

droplets are less than 1 mm, velocity would be 100 ft/sec+

characteristics of medium impact velocity blood spatter

droplets are 1-4 mm, velocity would be ~25 ft/sec

characteristics of low impact velocity blood splatter

droplets are 4+ mm, velocity would be 5 ft/sec

how to determine origin direction of spatter

direction tail of blood splatter is pointing to tells the origin direction. blood splatter with no tail is from a 90° angle

what is RI (refractive index)?

the ratio of the speed of light in a vacuum to the speed of light in another substance

how does density affect the speed of light?

when light travels from one medium to another, its speed changes relative to the density of the medium

what is one method to determine RI?

submersion

what is submersion?

place a glass fragment into different liquids of known RIs, and if the piece of glass and liquid have the same RI, the glass will look like it disappeared in the liquid

what is submersion with a low power of microscope?

use submersion method and put glass under low power microscope. If the RI of the liquid is different from the RI of the piece of glass, a becke line will form

what is a becke line

a halo-like ring that appears around the edges of the glass

why does a becke line appear?

refracted light becomes concentrated around the edges of the glass fragment

what is the RI of headlight glass?

1.47-1.49

What is the RI of TV glass?

1.49-1.51

What is the RI of window glass?

1.51-1.52

what is the RI of bottles?

1.51-1.52

what is the RI of ophthalmic (corrective) lenses?

1.52-1.53

what is the 3R rule for glass fractures?

Radial cracks form a right angle on the reverse side of the point of impact

what are radial cracks in glass fractures?

the first cracks to form; propagated in short segments on the opposite side of the force

what are concentric cracks?

secondary cracks that form from continued pressure on the same side as the force applied. terminate at radial cracks

How can you determine which hole/fracture was made first in glass analysis?

crack propagations are stopped by earlier cracks