FORENSICS EVIDENCE COLLECTION

A. Understanding Your Evidence

Patent Impression

The word ‘patent,’ means obvious or evident. Patent impressions are visible and usually need no enhancement such as fingerprint powder.

A patent impression occurs as the result of transferring a foreign material that has coated the skin of the fingers. Examples of foreign materials would be paint, tar, grease, blood, or ink. Patent impressions are photographed and the item that they are deposited on is collected if necessary.

Plastic or Molded Impressions

A plastic or molded impression is deposited when the hands, fingers, or feet are pressed into a soft rubbery type material that will retain the impression of the ridge detail. Examples of the materials where a plastic impression would be deposited are clay, wet paint, blood, or tar. Plastic or molded impressions are visible and need no powder or enhancement. They are simply photographed and if necessary the item is collected and may be caste.

Patent vs. Molded Impressions

"Is a bloody print the same as a print in blood"?

The answer to this question would be, "NO". The print in blood would be an example of depositing a plastic or molded impression into the surface of blood. The bloody print would be an example of a patent impression because the blood coating the hand or finger is leaving an impression, from the blood, onto another surface.

B. Proper Procedures for Collecting Impressions in a Crime Scene

[SH1] Blood that is in liquid pools should be picked up on a gauze pad or other clean sterile cotton cloth and allowed to air dry thoroughly, at room temperature. Seal [SH2] and label in the proper containers. Place only one item in each container. Do not use plastic containers. The sample should be refrigerated or frozen as soon as possible and brought to the Laboratory as quickly as possible. Delays beyond 48 hours may make the samples useless.

Dried Blood

Never attempt to wipe dried stains from an object using a moistened cloth or paper.

• If on clothing, if possible, wrap the item in clean paper; place the article in a brown paper bag or box and seal and label the container. Do not attempt to remove stains from the cloth.

• If on small solid objects, wrap the item in clean paper and send the whole stained object to the Laboratory, after labeling and packaging.

• If on large solid objects, cover the stained area with clean paper and seal the edges down with tape to prevent loss or contamination. If impractical to deliver the whole object to the Laboratory, scrape the stain onto a clean piece of paper, which can be folded and placed in an envelope. Do not scrape directly into evidence envelope. Scrape blood from objects using a freshly washed and dried knife or similar tool. Wash and dry the tool before each stain is scraped off. Seal and mark the envelope.

• Do not mix dried stains. Place each stain in a separate envelope.

[SH3]

ONLY FYI

Blood Samples From Live Individuals

For typing purposes, have sample drawn into properly labeled vacutainers. If the victim is injured to the extent that a transfusion is necessary, make an effort to obtain or begin necessary procedures to obtain the pre-transfusion sample collected by the hospital. These samples are not retained for long periods by the hospital, so it is important to act promptly. Also, make sure that some bloodstained garment worn by the individual has been air dried and frozen to serve as a secondary standard.

Handling and Storage of Physiological Fluid Evidence*

Stains and Controls

1. Air dry

2. Package in paper

3. Freeze

Consider special handling of non-absorbent items on (metal or plastic). Any condensation from thawing could disturb or destroy such evidence. Such items should be kept at room temperature and submitted to the lab as soon as possible.

*Parts of the information were adapted from an adaptation of information presented on the website: [SH4] . http://www.crime-scene-investigator.net/collect.html taken from the California Commission on Peace Officer Standards and Training's workbook for the "Forensic Technology for Law Enforcement" Telecourse presented on May 13, 1993.

We test for the presence of blood using phenolphthalein known as the Kastle-Meyer test. The Kastle-Meyer test is a highly sensitive method for detecting blood, even invisible to the naked eye. Phenolphtalein gives a positive reaction to all bloodstains that contain heme, which is the iron portion of the oxygen carrying pigment hemoglobin that is found in the red blood cells of vertebrates. Thus if the Kastle-Meyer test is negative, then there is no point in pursuing blood typing or other identification methods.

[SH1]Recovery

In recovering latent impressions there are numerous products available for the task. The techniques can be broken down into four simple areas. The conventional methods consist of mechanical and chemical development. The more modern techniques applied today in recovering latent impressions are florescent die stains or powders (aided with some type laser or light source), and superglue fuming. It should be noted that latent impressions on some surfaces may be fragile.

Mechanical Development

Mechanical development is the use of a brush and powder to physically dust the surface. This technique allows the particles of the powder to adhere to the contaminates which causes the ridge deposits. The mechanical development is for nonporous items and surfaces.

There are three types of brushes manufactured for the use of mechanical ridge detail development:

1. Fiberglass

2. Camel hair

3. Feather brush

There are an assortment of powders, lifters and tapes that are specially formulated and manufactured for the use of impression recovery.

Chemical

For protection and safety reasons these methods are applied in the laboratory under well ventilated conditions. A variety of chemicals are produced to react to certain components that make up the ridge deposits. More than a general knowledge of the chemicals as well as the contaminates in the deposits are needed to perform these tasks. The chemical processing techniques are for porous, absorbent items such as paper, untreated wood, and matte, semi-porous finished items.

Superglue Fuming

Cyanoacrylate ester is the active ingredient in superglue. It creates a vapor that polymerizes (creates a white residue) on contaminates such as latent impression deposits. Superglue is sold in a liquid or pouch form and comes in a variety of viscosity's. As documented by the US Army Crime Lab, superglue fumes are strongly irritating to the eyes and respiratory system. Personal Safety and caution are the keys to this development technique. The primary purpose of superglue in the field is to fix the impression on items where the latent impression may be fragile, so that it is less destructible during processing or transport. It does not make the impression indestructible. Without the proper caution the impression can still be wiped away or destroyed.

[SH1]

Evidence Collection Guidelines

This document provides evidence collection guidelines for the following types of evidence. Your agency's policies may vary. Please check with your supervisor if you have any questions.

Contents

Blood Stains

Controlled Substances and Medicinal Preparations

Questioned Documents

Latent Fingerprints

[SH2]Standard Blood Specimens/Autopsy Blood Samples

Request that pathologist obtain the sample directly from the heart into a yellow (ACD) or purple stoppered vacutainer (some labs request both). In rare cases when no liquid blood is available, ask pathologist to collect a section of liver, bone, and/or deep muscle tissue and freeze for typing. In such cases, proceed also with collection of a secondary standard as described below.

• If close to the Laboratory, deliver stained object immediately.

• If unable to deliver to the Laboratory, or if the object must be mailed, allow the stain to air dry completely before packaging.

• Do not heat stained material or place it in bright sunlight to dry. Hang clothing and similar articles in a room where there is adequate ventilation.

• If not completely dry, label and roll in paper or place in a brown paper bag or box and

[SH3](Obligation under People vs Nation and Hitch that a reasonable and good faith effort be made to preserve perishable evidence)

[SH4]

back