Physical Evidence

Category: Education

Presentation Description

No description available.


Presentation Transcript

Physical Evidence :

Physical Evidence How do we collect and identify physical evidence?

Review What types of things should be in a finished or polished crime scene sketch?:

Review What types of things should be in a finished or polished crime scene sketch?

Introduction to Physical Evidence The Value of Physical Evidence (reading):

Introduction to Physical Evidence The Value of Physical Evidence (reading) Recognize, Collect, & Preserve The roles of Physical Evidence: Reconstruct the Crime Scene & Sequence of Events Determine whether or not a crime occurred. Link an individual with another or with a crime scene Provide Investigative Leads to Investigators. Provide facts to a jury which may assist in the determination of the guilt or innocence of an accused. Provide evidence to link serial homicide or rape case.

Advantages of Physical Evidence:

Advantages of Physical Evidence Provides a tangible object for the jury to see Can be taken into the jury room The defendant cannot distort the physical evidence. Some cases cannot be solved without the physical evidence Physical evidence is not subject to memory loss The defendant can have the evidence tested by an independent expert.

Evidence- anything that can be used to determine whether a crime has been committed.:

Evidence- anything that can be used to determine whether a crime has been committed. Materials collected and scientifically analyzed to determine the nature and circumstances of a crime. Direct-establishes a fact (eyewitness) Circumstantial- provides an inference about what happened (more reliable than direct) IDENTIFICATION To determine the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit. What is it? COMPARISON Subjecting a suspect specimen and a standard (reference) specimen to the same tests and examinations for the purpose of determining whether or not there is a common origin. Does it Match?

It is imperative to conduct a thorough collection and scientific evaluation of physical evidence for all criminal investigations. Physical evidence can be used to link an individual to a crime or to exonerate a person from suspicion.:

It is imperative to conduct a thorough collection and scientific evaluation of physical evidence for all criminal investigations. Physical evidence can be used to link an individual to a crime or to exonerate a person from suspicion . Common Types of Physical Evidence: (Biological Evidence = B and Physical Evidence = P) Blood, Semen, and Saliva (B) - Impressions (P) Documents (P) - Organs & Body Fluids (B) Drugs (P) - Paint (P) Explosives (P) - Petroleum Products (P) Fibers (P) - Plastic Bags (P) Fingerprints (P) -Plastic, rubber, & polymers Firearms and Ammunition (P) - Powder Residues (P) Glass (P) - Serial Numbers (P) Hair (B) - Soil & Minerals (P) Tool Marks (P) - Vehicle Lights (P) -Wood and plant matter (B)

Physical Evidence Characteristics:

Physical Evidence Characteristics Class Characteristics Properties of evidence that can only be associated with a group and never with a single source. The “product rule” is often used to calculate the overall frequency of an occurrence in a population. (multiply the frequencies of independently occurring genetic markers) Individual Characteristics Properties of evidence that can be attributed to a common source with an extremely high degree of certainty or probability. The practical and personal experience of the examiner supports or negates the significance of these evidence characteristics.

Class Characteristics:

Class Characteristics Creation and updating of databases Can corroborate events, eyewitness accounts, confessions, and informant testimony Must be free of human error and bias Must exhibit a significant amount of diversity When do class characteristics become individual characteristics?

Individual Characteristics:

Individual Characteristics Criteria somewhat subjective More specific and detailed Sophisticated techniques and improved technology have minimized the limits of identification. Could become too particular that they could negate identification of evidence from its source due to natural variations.

Identifying Physical Evidence:

Identifying Physical Evidence Presumptive Tests Identify suspect evidence (class) Cheaper Faster Can be done at crime scene Less training needed Help focus investigation Specific Tests Can lead to individual classifications Costly Time consuming Typically done in the lab More exact procedure Match a suspect to a crime

Evidence Collection Guidelines Click the link below to learn more about how to collect that type of evidence.:

Evidence Collection Guidelines Click the link below to learn more about how to collect that type of evidence. Blood Stains Dried Blood Stains Stains and Controls Saliva Hair Fibers and Threads Latent Fingerprints Marking Preservation Questioned Documents Preservation of Questioned Documents Charred Documents Other Questioned Document Evidence Exemplars Tool Marks Preservation and Packaging of Tools Preservation of Tool Marks

Blood Stains:

Blood Stains 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. It 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. Refrigerate, do not freeze standards collected in yellow stoppered vacutainers . 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 seal and label container. Place only one item in each container. Do not use plastic containers.

Dried Blood Stains:

Dried Blood Stains On clothing, if possible, wrap the item in clean paper, place the article in a brown paper bag or box and seal and label container. Do not attempt to remove stains from the cloth. On small solid objects, send the whole stained object to the Laboratory, after labeling and packaging. Do not mix dried stains. Place each stain in a separate envelope . Never attempt to wipe dried stains from an object using a moistened cloth or paper. 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.

Stains and Controls:

Stains and Controls 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. Air dry Package in paper Freeze


Saliva Collect on a sterile gauze pad or swabs, allow to air dry and package in paper. Do not use plastic containers. Air dry Package in paper Freeze


Hair An examination of human hair can occasionally reveal the possible race of the individual from whom it came and the part of the body from which it originated. Human hair can be compared to determine whether or not two samples could have had a common origin. The value of the Laboratory examinations of such specimens will depend upon the amount of hair recovered and the characteristics found in the examinations. If hair is attached, such as in dry blood, or caught in metal or a crack of glass, do not attempt to remove it but rather leave hair intact on the object. If the object is small, mark it, wrap it, and seal it in an envelope. If the object is large, wrap the area containing the hair in paper to prevent loss of hairs during shipment. Recover all hair present. If possible, use the fingers or tweezers to pick up hair, place in paper bindles, coin envelopes, or specimen jar which should then be folded and sealed in larger envelopes. Label the outer sealed envelope.

Fibers and Thread:

Fibers and Thread Such evidence is often found in fabric abrasions or caught in torn materials or other areas on hit-and-run vehicles. In some burglary cases, it may be found caught in torn screens, broken glass, or other locations . Examination of fibers can normally be conducted to determine the type or color of fiber. Such examinations will sometimes indicate the type of garment or fabric from which they originated. Fibers and threads can also be compared with suspects clothing to determine whether or not they could have come from this clothing. If threads or large fibers are found, they can often be picked up with the fingers and placed in a paper bindle, then in a coin envelope, which can be sealed and marked. Never place loose fibers directly into a mailing envelope since they can be lost from this type of envelope. Collect on a sterile gauze pad or swabs, allow to air dry and package in paper. Do not use plastic containers. If the fibers are short or few in number, and if it is possible to do so, wrap the area or the entire item containing the fibers in paper and send the whole exhibit to the Laboratory. Pick up fibers on tape only if the laboratory in your jurisdiction allows it and gives you its requirements. When fibers or threads are recovered, always send all clothing of persons from which they might have originated to the Laboratory for comparison purposes.

Latent Fingerprints:

Latent Fingerprints Marking of Latent Fingerprint Evidence All such evidence should be marked in some distinctive manner, such as is the case with any other type of physical evidence. Precautions should be taken, when marking evidence, not to damage or destroy potential latent fingerprints. Lifted, developed latents should also be marked or sealed in marked envelopes. Photograph-developed latents with and without identifying markings and scale.

Latent Fingerprints:

Latent Fingerprints Preservation of Fingerprint Evidence The primary precaution in all cases is the prevention of adding fingerprints to evidence, or of destroying those already present. Most fingerprints submitted will be on paper, glass, metal, or other smooth surfaced objects. When articles containing latents must be picked up, touch as little as possible, and then only in areas least likely to contain identifiable latents, such as rough surfaces. While gloves or handkerchiefs may be used to pick up such exhibits, any unnecessary contact should be avoided. Although using a cloth to pick up exhibits prevents leaving additional prints on the articles, the cloth will frequently wipe off or smear any prints originally present, unless great care is taken.

Latent Fingerprints:

Latent Fingerprints Preservation of Fingerprint Evidence Large articles containing latents such as glass, metal articles, and firearms should be placed on wood or heavy cardboard and fastened down with string to prevent shifting and contact with other objects in transit. Where such evidence is to be examined frequently, a pegboard should be obtained on which wooden pegs can be moved as desired to support exhibits and keep them from moving. Bottles and glasses may be placed vertically on a board and placed in the bottom of a box. The base of the bottle or glass can be surrounded with nails to hold it in place, and the top can be either inserted through a hole in a piece of cardboard or held in position with a wooden board nailed to the container's lid. Papers and documents containing latent prints should be placed individually in a cellophane or manila envelope. Such a container can be sandwiched between two sheets of stiff cardboard, wrapped, and placed in a box for mailing .

Questioned Documents:

Questioned Documents Questioned Material to be Submitted All questioned documents involved in a particular investigation should be submitted to the Laboratory for examination. This is important since questioned documents are identified by a comparison of similarities, plus an absence of divergences or dissimilarities. In order to make an identification, sufficient handwriting, typewriting, or other evidence must be available on which to base an opinion. This means that all questioned material is needed, as well as sufficient exemplars or known specimens.

Questioned Documents:

Questioned Documents Preservation of Questioned Documents Under no circumstances should either the questioned document or the exemplars be marked, defaced, or altered. No new folds should be made, nor should marks or notes be placed on such material. Personal marks for identification purposes should be made as small as possible on the back or other area of the document where no handwriting or typewriting is present. Whenever possible, all documents should be protected by placing them in cellophane or plastic envelopes.

Questioned Documents:

Questioned Documents Charred Documents Where examination and decipherment of charred paper is involved, great care must be taken to prevent any additional crumbling or breaking apart of the burned material. Normally it should be placed on top of loose cotton in a box and delivered in person to the Laboratory. No matter how it is packaged, such material will be damaged if attempts are made to ship it by mail.

Questioned Documents:

Questioned Documents Other Questioned Document Evidence In addition to handwriting and typewriting comparisons and the decipherment of charred documents, many other related examinations can be conducted by the Laboratory. These include, but are not limited, to : Restoration or decipherment of altered, obliterated, or erased writing . Comparison of check protectors and rubber stamps with questioned printing . Identification of embossed or indented writing or typing . Comparison of paper and commercially-printed material, such as checks, coupons, receipts, and others . Physical matching of cut or torn paper of various types . Problems relating to inks.


Exemplars It is very important to have sufficient handwriting exemplars for comparison with the questioned document. One or two signatures on a suspect's driver's license or a draft card, in many cases, does not contain sufficient individual characteristics on which to base a conclusion. In some instances, such an examination may substantiate a suspicion and this should be considered as an investigational lead. To support this, it is necessary to obtain and examine additional standards.


Exemplars Collected specimens that were made in business transactions such as receipts, promissory notes, credit and employment applications, letters, booking card, and fingerprint card signatures are writings that, in most cases represent the individual's most normal writing. It is significant in many cases that these writings be of the same date as the questioned document. It is important to obtain request specimens from a suspect at the first interview; the suspect may be uncooperative at a later date.


Exemplars The conditions surrounding the preparation of the questioned document should be duplicated as nearly as possible when the request exemplars are obtained. If yellow-lined paper and blue ink were used to produce the questioned document, the same or similar color and type of paper and instrument should be used. If the suspect document is a threatening letter and the note is either handwritten or block lettered, the same style should be requested from the writer. Have subjects write their names and addresses several times and brief personal histories. This should be removed and another sheet of paper furnished. Dictate the exact words and numbers which appear on the questioned document. this should be done at least 12 times, removing the specimens from the writer's view as they are produced. If it is a check case, the specimens should be taken on blank checks or slips of paper of the same/appropriate size. The number of specimens necessary for an identification in any specific case cannot be determined; therefore, at least twelve specimens should be obtained for each questioned document.


Exemplars When securing typewritten exemplars, several copies of the questioned documents should be made on the suspected machine using light, medium, and heavy touches. At least one copy should be made with the ribbon removed from the machine, or the ribbons set on stencil, and the keys allowed to strike directly on a sheet of new carbon paper, which should be inserted on top of the paper used for the specimen. This provides clear-cut exemplars of any machine's type face, showing disfigurations in type characters. Always type the exemplars on the same type and color of paper as that used on the questioned document.

Tool Marks:

Tool Marks Tool marks are encountered most frequently in burglary cases but may also be found in other types of crimes. The evidence consists of striations or impressions left by tools on objects at the crime scene and various types of tools found in the possession of suspects. In other cases, it is possible by means of physical and other comparisons to prove that parts of tools left at crime scenes were broken from damaged tools found in the possession of suspects. In many cases, it is possible to identify the specific tool which made the questioned marks by means of a Laboratory comparison of tools and marked objects. In some instances, it is also possible to prove that marks of various types on tools were produced by objects which they contacted at crime scene.

Tool Marks:

Tool Marks Preservation and Packaging of Tools All areas on recovered tools which contain transferred paint, building material, or other contamination should be wrapped in paper and packaged to prevent the prying blades or cutting edges .'rom contacting any other surface or object . Attempts should never be made to fit tools into questioned marks or to make test marks prior to Laboratory examination. If done, the questioned mark or tool may be altered and this may make any Laboratory examination valueless. In addition, traces of transferred paint or other stains on the tool may be lost or additional material may be transferred to the tool.

Tool Marks:

Tool Marks Preservation of Tool Marks Whenever possible, submit the whole object containing tool marks to the Laboratory instead of just removing the area containing the mark. If this is not possible, carefully photograph and sketch the area containing the mark. Although this photograph will not be sufficient to allow the Laboratory to perform a tool mark comparison with the tool, it will assist the Laboratory to determine how the mark was made so that test marks can be-more easily made.

Tool Marks:

Tool Marks Preservation of Tool Marks Casts of tool marks can be made by a person who has had considerable experience in this work. Poor casts are useless for comparison purposes and some marks will be damaged if improper methods are used. Pack the object containing tool marks so that no alteration or damage will occur during shipment. Small objects should be wrapped with clean paper and placed in envelopes or boxes, while important areas on larger objects can be protected with paper. Whole, large objects can be packed in cartons or crates, if not delivered in person .

authorStream Live Help