Date of Award
Doctor of Philosophy
Mark D. Dadmun
John Turner, Roberto Benson, Jimmy Mays
The cyanoacrylate fuming method (CFM) is the standard method for forensic investigators to develop latent fingerprints from nonporous substrates. Variations in the effectiveness of the technique and the quality of the ethylcyanoacrylate (ECA) polymer impression formed during the development process have lead researchers to investigate the fundamental reactions between the print residue and the developing vapor. Identification of the active initiating species in the residue is an essential first step to understanding the development process. The fingerprint residue is composed primarily of water and eccrine salts, of which, water is generally accepted as the active initiator. However, initiation by water alone fails to adequately explain variations in the characteristics of the polyethylcyanoacrylate formed, such as molecular weight and morphology.
It is shown that the anionic eccrine salts (lactate and alanine) and not water are the active initiators of the ECA fumes in the fingerprint residue. The two most abundant functionalities present in the eccrine salts, primary amine and carboxylate, are then isolated as model surfaces and their ability to initiate the polymerization of ethyl-cyanoacrylate fumes was documented. Surfaces containing monolayers of carboxylic acid functionalities are found to be significantly more effective at initiating the ECA vapor than surfaces comprised of monolayers of primary amines. Additionally, a direct correlation was established between the rate of termination in a growing ECA polymer chain and the ionic conditions at the initiating surface. Optimizing the surface conditions to a more basic environment significantly enhanced the deposition rate of ECA polymer onto the initiating surface.
The understanding obtained in these model studies is then applied to real latent fingerprints and how the changing print conditions affects development by the CFM is examined. The two main types of latent prints, eccrine and sebum-contaminated eccrine prints are often reported to produce polymer impressions of differing quality. Comparison of the molecular weight characteristics of the ECA polymer formed during print development found that the presence of sebum in the print residue limits molecular weight of the polymer grown.
Additionally, the quality of the polymer impression obtained from latent fingerprints is known to decrease the longer the print is aged prior to development. The effect of print aging on the polymer deposition kinetics as well as the characteristics of the resulting ECA polymer was explored to establish if the decrease in developed print quality is a result of changing polymerization conditions. The loss in development quality with aging is reported to not be chemical in nature but possibly a result of physically weathering the surface. Exposure of the latent prints to air currents during the aging process is found to be a critical variable leading to the reduction of the amount of polymerization that occurs on the print residue surface.
In an effort to restore the ability of a degraded print to polymerize ECA fumes, the surface environments of aged latent prints were manipulated by exposing the prints to either acetic acid or ammonia vapor prior to print development. Both the acetic acid and ammonia vapors were found to increase the amount of ECA ploymerization that occurs on the surface. The acetic acid was found to be significantly more effective at increasing the amount of polymer growth onto the fingerprint ridges even when the time exposed to the acetic acid was one half the time a print was exposed to ammonia vapor. Finally, the greater enhancement observed in the acetic acid exposed prints suggests that the enhancement method generates a coating of the enhancement agent across the fingerprint ridges and that it is this coating that initiates the ECA fumes.
Wargacki, Stephen Paul, "Understanding and Controlling the Molecular Level Processes Involved in the Development of Latent Fingerprints Using the Cyanoacrylate Fuming Method. " PhD diss., University of Tennessee, 2005.