When an object comes in contact with a surface there is the potential for characteristics of the object to be transferred to that surface. This may occur by the object impressing its shape into the surface, or by material on the object or surface (dust, blood, dirt or other matter) being transferred between the surface and object and leaving a visible print on the object, the surface or both. These visible impressions, or patent prints, left at a scene can be used to link the observed marks to a class of objects or, if sufficient detail is present and recovered, to a specific object.
Types of evidence that may produce such impressions include, but are not limited to, marks produced by the following types of objects making contact with a receiving surface:
3. Tire treads
Additionally, objects left at a scene may possess manufacturing marks (including, but not limited to, extrusion marks on wire or wire insulation and rolls of plastic bags) that may be used to link them to similar material from a suspect.
When practical, it is desirable to submit the item bearing the impression or patent print to the laboratory for examination. Due to the variety of objects that may bear impressions or patent prints, this is frequently not practical. The Team Leader uses judgment in determining if future comparative examinations will benefit from the submission of the actual item (if possible), or if a cast or lift along with scale photographs and other documentation from the scene, will be sufficient In either case, documentation of the location of impression or patent print, with scale, can provide forensically significant information useful in future comparative examinations.
Impressions and patent prints are often associated with trace evidence
, latent prints
and/or other types of evidence. Evidence should be handled in a manner that protects and preserves the most fragile type of evidence associated with the item in question.
i. Electrostatic Dust Print Lifter
ii. Dental Stone Casting Material
iii. Sulfur Casting