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Post by hope on Aug 22, 2021 10:33:05 GMT -6
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Post by hope on Aug 22, 2021 10:41:40 GMT -6
I found that research study on the longevity of latent fingerprints on lightbulbs. Unfortunately, it is copyrighted journal and for educational & research purposes only. So, I don't believe I can post the actual paper here. It is also behind a paywall.
Here is a summary:
The purpose of this study was to determine if it was possible to determine when a fingerprint was deposited on a surface. If newer prints would result in a higher quality score and older prints a lower quality score.
Background:
"In the fall of 2016, the Henrico County Police Department in Richmond, Virginia encountered a case in which latent fingerprints from a defendant accused of burglary were recovered from a light bulb. The defended asserted that he touched the bulb years prior to the crime and published literature offered no research to support or disprove his claims concerning the potential age of the print."
"This study addresses how the length of time latent fingerprints are exposed to heat from a 60-watt incandescent light bulb potentially effects the quality for identification and determining age of deposition. "
Fingerprints are a mixture of sebum from sebaceous sweat gland and water, amino acids, fatty acids & inorganic salts from eccrine glands. Plus contaminates such as dirt, cosmetics, blood. Serine is the most abundant amino acid and it can withstand temperatures of 150° C. Fatty acids such as asiatic acid and oleic acid can withstand temperatures of 250° C. Fingerprints have survived on various nonporous items following exposure to temperatures of 600° C (such as arson cases). In such cases, rather than burn off under such intense heat, fingerprints on metal surfaces have been shown to corrode the metal leaving a durable print for collection.
60-watt light bulbs were chosen for the study because prior to LED bulbs, they were the most popular bulb in the U.S. and because of the heat they generate. Multiple units were constructed, each with 10 light bulbs. The bulbs were cleaned & placed in the light sockets while wearing gloves. 9 fingerprints were applied to each bulb by the same donor. Prints were deposited to the top, middle and bottom portion of the bulb.
The units were each powered for different lengths of time. 9 of the 10 bulbs were powered. Fingerprints were applied to the 10th bulb, however, it was used as the control bulb and not powered.
Here are the lengths of burn time used for each unit:
• 18 hours
• 48 hours
• 72 hours
• 120 hours
• 168 hours
• 336 hours
• 504 hours
• 672 hours (1 month)
Thermal imaging was used throughout the process to record surface temperature. The top of the bulbs was the hottest at 156.3° C. The middle was 112.6° C and the bottom 62.7° C. A total of 676 prints were collected . Fingerprints were then given a quality score, ranging from 1 - 10.
The overall mean quality score was highest for prints from the middle of the bulb (5.6). The bottom of the bulb had a mean score of 4.5 and the top had a mean quality score of 4.1. Each location had prints that scored higher (as high as 8 for the middle of the bulbs) and some that scored poorly. The differences occurred irregularly and without any noticable trends. Concluding, "this reinforces the complexity of interpreting cause and effect for fingerprint quality, as fingerprint deposition is variable even in a controlled environment."
The fingerprints did not show a decrease in quality score based on the number of heating hours, ie the hottest temperatures did not yield the lowest scores. Which leads to the conclusion that "the mean quality scores of all three temperature classes are within one standard deviation of one another, reaffirming there is no way to estimate the of a print based on its quality after heat exposure. "
Conclusion:
"The results of this study led to the conclusion that latent fingerprints recovered (with black powder and tape lifting) from heated 60-watt incandescent light bulbs cannot be aged on the basis of of the recovered fingerprint quality, for heating periods of 18-672 h."
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