Before we use any assay, we must ask some critical questions. If we do not know the answer to these questions, how could one use the assay to put someone in jail (or acquit thereof).
-How long after semen exposure, Semenogelin can be detected? 24 hr, 48 hr, 72 hr? Has this been evaluated under various scenarios?
-What concentration of Semenogelin corresponds to semen exposure? Assay used to determine it? Does a reference standard exist for it? If not, it is an issue.
-What concentration of Semenogelin is detected by RSID Semen? How often it may yield false negative? How often it may yield false positive? Study published by Hobbs (2010) tested 581 vaginal swabs. RSID Semen test gave false negative test results in 46% of the cases (Table 2, page 294).
-What reference standard can be used to quantify the sensitivity of Semenogelin test? You cannot establish a sensitivity of a test with microliters of semen as Semenogelin will likely vary from person to person, with time and with environment.
-Specificity and sources of false positives. What other body fluids/tissues may have Semenogelin present and the secretions thereof?
--- On Fri, 14/1/11, Jack Walker <jackwalker29@ymail.com> wrote:
From: Jack Walker <jackwalker29@ymail.com>
Subject: Re: [Forens-l] Man Accused of Sexual Assault Released After 16 months in Jail: U.S.A. v.s. Theodore Largo
To: forens@geradts.com
Cc: forens-dna-owner@yahoogroups.com, forens-dna@yahoogroups.com, forensic-science@yahoogroups.com
Received: Friday, 14 January, 2011, 10:08 AM
Granted that Seratec PSA Semiquant has false positive issues and is quite possible that it was a false positive. However, isn't it also possible that Semenogelin test was a false negative test result. The news article mentions that Semenogelin is specific to semen, but it is not.. You know what, I am not even sure if the immunoassay technology is reliable for forensic casework, the most bizarre one was when RSID Saliva was giving false positive with the buffer in the kit. How many more may be in jail due to such bizarre results? Does this mean that many of the sexual assault cases done so far should be looked at all over again?
From: Roger Sealy <roger.sealy@yahoo.com>
To: forens@geradts.com
Sent: Fri, January 14, 2011 1:45:31 PM
Subject: [Forens-l] Man Accused of Sexual Assault Released After 16 months in Jail: U.S.A. v.s. Theodore Largo
Mr. Stephen D. Aarons (Santa Fe, New Mexico) was the assigned public defender for a Navajo man named Mr. Theodore Largo. Up until the week of the trial, July 26-29, 2010, Theodore had been sitting in jail for 16 months. In Federal Court, the FBI crime lab's enormous interpretive flaws were fully dissected in front of the jury. Mr. Largo was found not guilty on all counts and immediately released.
The prosecution's scientific case was simple: 4 anal swabs had been collected from a young alleged victim. The FBI lab report stated "….semen identified". Mr. Aarons contacted SFR to examine the FBI lab report. Dr. Spence immediately asked Mr. Aarons to request discovery - all of the supporting scientific documentation. The FBI lab documents pointed to a "Faint Positive" screening test on two of the four swabs. Defying logic, NO effort was made to identify sperm cells on the evidence swabs via microscopic searches. Instead, they proceeded to test ONE of the four swabs for DNA. This strategy revealed NOTHING suggesting the possible presence of Mr. Largo's DNA. Despite this glaring chasm in their scientific case, FBI Lab management refused to back off from their conclusion of "….semen identified".
Dr. Spence informed Mr. Aarons that the FBI lab's conclusions were entirely unjustified, inappropriate, and an enormous misrepresentation of the scientific facts. Dr. Spence backed up that opinion by having the swabs tested (Independent Forensics, Hillside, Illinois) with a more accurate, SPECIFIC screening test for semen, as well as a more sensitive, more thorough DNA testing strategy. The independent outsource lab revealed NO indication of semen and SUPPORTED the FBI Lab's finding of NO DNA linking Mr. Largo to any criminal act.
The screening test utilized by the FBI lab was an ultra-sensitive detection system for a protein that is abundant in semen, ....prostate specific antigen (PSA). The error of leaning too heavily on a PSA test is that recent years have revealed the presence of PSA in body tissues and fluids OTHER than semen. For the defense, the PSA and ZERO DNA issues were illuminated by Richard Coughlin, Ph.D. (President/Chief Scientific Officer of Sequela, Falmouth, Maine), Karl Reich, Ph.D. (Chief Scientific Officer, Independent Forensics), and Michael Spence (Spence Forensic Resources). Refer to the link for elementary information addressing the forensic detection of PSA.
The prosecution's entire scientific case hinged upon a $1.05 PSA detection cartridge produced by Seratec, a German biotech company. Hidden in the FBI's documentation was the "FT POS" notation, indicating the apparent presence of ONE protein. NO attempt was made to find any sperm cells, and two laboratories revealed a conspicuous ABSENCE of any incriminating DNA. It was no surprise that the jury took only a few hours to grant Mr. Largo his immediate release.
There is nothing fundamentally wrong with the PSA tests, ....when they are employed strictly as screening tools, ….pointing the way to the Holy Grail of Forensic Biology, …….DNA. PSA is anything but THE de facto means to establishing a crime. Management associated with ANY forensic biology lab (law enforcement or private enterprises) should interpret certain data with extreme caution.
http://www.spenceforensics.com/fascinatingcases.html
-----Inline Attachment Follows-----
_______________________________________________
Forens mailing list
Forens@box528.bluehost.com
http://box528.bluehost.com/mailman/listinfo/forens_geradts.com
[Non-text portions of this message have been removed]
To unsubscribe send a blank e-mail to: forensic-science-unsubscribe@yahoogroups.com
Group home page: http://groups.yahoo.com/group/forensic-science
From the home page you can search the list archives. It also includes links to forensic science sites and allows you to modify your account settings.
0 comments:
Post a Comment