NCJ Number
90297
Date Published
1981
Length
19 pages
Annotation
This report describes the technique for using a reagent called a physical developer to use subsequent to the application of ninhydrin where ninhydrin has failed to produce useful fingerprints on paper.
Abstract
Ninhydrin is the most commonly used reagent for the visualization of latent fingerprints on paper; however, there are instances when treatment with ninhydrin will not show useful marks because some people do not deposit sufficient quantities of amino acids to produce a visible reaction with ninhydrin or because the paper may have been kept in a humid atmosphere or wetted since a mark was deposited. A reagent called physical developer (PD) has been developed by Great Britain's Atomic Weapons Research Establishment under contract to the Police Scientific Development Branch for use when ninhydrin fails to yield prints. The PD reagent contains silver ions, a ferrous/ferric redox system, a buffer, and detergent in an aqueous solution. The detergent prevents the premature deposition of silver metal. When paper is immersed in this solution, metallic silver is deposited on its surface. Usually, if any fingerprints are present, the silver metal is preferentially deposited on them; they develop as dark gray images on a lighter background. While the components in the fingerprint deposit which are sensitive to PD have not been identified, they are supposed to be waxy or fatty material. Detailed discussions are provided for the procedure of incorporating PD into the examination of paper, the preparation and use of PD, and the radioactive toning process. Appended are an equipment list, chemicals, useful addresses, and eight bibliographic listings.