Examination Techniques

You should arrange for guards to be posted to prevent damage to evidence until you have had time to examine the evidence thoroughly. Make sure doors, windows, transoms, and other openings with hinged or sliding doors or covers are not opened, closed or handled in any way likely to destroy or mar minute tool marks or fingerprints.

Carefully examine every door, window, transom, skylight, and other opening that may have been used by a criminal as a means of entry or exit. Tool marks are likely to be discovered at these points, particularly when forcible entry or exit has been made.

Pay particular attention to broken, forced, or cut locks, latches, and bolts, and the immediate area surrounding these fastenings. Systematically search the entire crime scene and its vicinity for the tool that may have been used. Also examine safes, cabinets, desks, chairs, tables, or ladders for marks.

Tool marks are preserved even if no tools are found at the crime scene-the tools that made the marks may be discovered later. Tool marks and tools should be immediately and carefully noted and pertinent information recorded. Include them in any photographs and sketches of the crime scene.

A tool mark should be photographed as soon as possible.

The tool mark should be examined visually to determine its gross appearance. This will provide information concerning the type or shape of the tool you _{are to look for.} The gross appearance of a tool impression may not be complete or well defined. For example, a hammer impression on a steel safe may not include the edges of the hammerhead, so the shape of the head cannot be determined. In this case, all suspect tools that could have made the mark must be sent to the laboratory for comparison purposes.

If the surface bearing an impression of a tool mark has been painted, a careful examination may reveal that flakes of paint have been removed and maybe adhering to the tool making the impressions. That may enable you to eliminate a number of possible suspect tools. The pattern formed by the removal of the flakes of paint may also be of value. If a tool is found bearing paint similar to that of the painted surface and the flake pattern appears to be identical in formation, the paint pattern formation should be photographed since some of the flakes of paint might be loosened and accidentally removed from the tool while in transit to the laboratory. The accurate matching of the pattern of paint on the tool with the pattern of the impression may be conclusive proof that the tool made the impression.

The tool should never be fitted into the tool mark to see if it could have made the impression. Such a procedure may prevent the admittance in court of any evidence concerning the tool and its marks, or the paint on it and the object.

Processing Evidence

A decision must be made as to whether the tool mark is to be removed for transmittal to the laboratory. The removal of a tool mark for comparison at the laboratory is highly desirable. Wholesale removal of property or integral parts of valuable structures is neither desirable nor necessary. This is a judgment area and your decision should be based on the following factors:

. Importance of the case. 

. Importance of the tool mark in comparison with other available evidence. 

l Distance of the crime scene from a criminal investigation laboratory. 

. Whether the tool-marked object belongs to the U.S. Government. 

. Courses of action. You now have three possible courses of action:

- Remove the original evidence or the desired portion.

- Cast and/or mold the evidence.

- Request that an examiner from a criminal investigation laboratory come to the scene and develop the evidence.

In considering these courses of action, you should also weigh the substantiating value of the original evidence.

Original evidence is more useful for scientific examination and evaluation and is less subject to attack in court than reproductions. You may often be unable to make photographs and casts that represent the evidence sufficiently for identification purposes at the laboratory. In fact, some authorities recommend that casting or other methods of taking impressions of a tool mark should be used only as a last resort.

A casting can never be equal to the original impression. That is particularly so with tool marks made in soft materials such as wood, putty, paint, and so on since many of the casting media most suited for these materials will not reproduce the fine details needed for identification. Experiments have shown that scratches in paint caused by minute irregularities in the edge of a tool cannot be reproduced by an impression or a cast. However, if the original mark is compared with one made directly by the tool, the full proof against the criminal may be obtained.

If a tool mark can be removed for transmittal to a laboratory, you should take several precautions. A sufficiently large piece of the object should be removed to prevent damage to the tool mark through splintering, bending, twisting, or abrading. Any tools found at the crime scene should also be transmitted to the laboratory with the items or original evidence.

An item removed as evidence should be clearly marked with the case number, your initials, and the date and time of removal. The evidence should also be marked to show the inside, outside, top and bottom surfaces, and the area bearing the tool mark.

You may remove, for example, such evidence as the marked portion of a door, window sash, windowsill, or doorsill and that portion of the window or door frame adjacent to the marked area; and any window latch, door latch, bolt, hasp, or lock that has been cut, broken, or forced for entry.

If the surface bearing the tool mark is painted, samples of the paint should also be transmitted to the laboratory. In many cases, even though no paint can be seen adhering to the tool, enough minute particles may be recovered from the tool to permit analysis and comparison at a laboratory.

It is sometimes possible to furnish the laboratory examiner information concerning the angle in which the tool was held when it made the mark. If this determination is possible, information concerning the angle formed by the tool and the surface of the object and the angle of deviation from the longitudinal direction of scrape marks, will materially assist the examiner.

If a tool mark is on metal and cannot be removed, samples of the metal should be obtained and transmitted to a laboratory. Particles of metal may adhere to the tool, in addition to the paint, and may be analyzed and identified by the laboratory examiner.

If cut pieces of wire are to be sent for examination, the suspect end of the wire should be clearly marked. Wire obtained for laboratory examination, should not be cut with the suspect tool.

Stolen articles, such as automobile radios, that cannot be positively identified by the owner can often be identified as being originally mounted in an automobile by matching cut ends of the wire remaining attached to the automobile to those on the radio.

You should carefully photograph a tool mark before it is moved, cast, molded, disturbed, or altered in any way. Photographs provide a permanent record of the evidence in its original state and location, identify original evidence with any casts or molds that may be made, and satisfy legal requirements for records of original evidence.

You should take photographs to show the tool marks and enough of the surface on which it is located to identify them positively.

Initial photographs should show the mark as it actually appears and its overall relationship to other objects at the scene. You should include an ordinary ruler and marking data in each picture to provide the laboratory examiner a scale of measurement for examination and comparison purposes.

Make a cast or a mold from a tool mark only when you have good reason for not removing the original evidence.

An impression found on wood or on a metallic surface may be cast with modeling clay or plasticize. These materials do not require any special preparation before use, nor are they likely to damage a tool mark if the frost casting attempt is unsuccessful. A reproduction of the tool mark itself maybe made from this cast using ^{plaster of Paris.} Ordinarily, it is not necessary to reproduce a mark on a wooden surface because of the ease with which the original evidence may be removed.

When it is necessary to make a cast of a mark the material best suited for reproduction will be determined by the shape and type of mark to be reproduced. Flat tool marks, hammer marks, chisel cuts, and pry marks may be reproduced using a variety of materials. Tool marks in wood, where undercuts are present, will have to be reproduced with a flexible material.

Suitable media, by brand or generic name, include the following:

Kerr Permlastic

Silicone rubber

Dow Corning Silicone Rubber RC 900

Kerr Perfection Impression Compound

Plasticize

Castoflex

Moulage and Posmoulage

Wood's metal

Plaster of Paris

You should not attempt the casting or molding of a tool mark unless you have repeatedly practiced the particular method on a similar wooden or metallic surface of no evidentiary value. Take sufficient care and time to ensure a usable reproduction. Never release the surface bearing the tool mark until you have obtained an accurate reproduction and cleared the release with appropriate legal authorities.