Scientific Testimony: An Online Journal


UCI Professor Finds DNA Laboratory Errors That Sent Wrong Man to Prison

For Immediate Release, March 11, 2003

UCI Professor William C. Thompson has played a key role in uncovering a miscarriage of justice that sent a Houston man to prison for a rape he did not commit.   Thompson, who is a professor in the Department of Criminology, Law & Society, has studied and written about forensic DNA evidence for over fifteen years.  He uncovered the error while helping a group of news reporters investigate allegations of fraud and incompetence in the Houston Police Crime Laboratory.

In July 1999, Josiah Sutton, then 16 years old, was convicted of rape based largely on DNA tests performed by the Houston Police Crime Laboratory.  Thompson reviewed the evidence in Sutton’s case in January and found a serious problem.  “The jury was led to believe that the DNA evidence uniquely identified Sutton as one of two rapists,” Thompson said.  “In fact, when correctly interpreted, the DNA evidence showed it was very unlikely that Mr. Sutton could have been one of the rapists.” 

Thompson’s criticism of the evidence prompted the Houston police department to hire an independent laboratory to re-test a semen sample collected from the rape victim.  On Monday, Sutton’s attorney announced that the new DNA test, which employed more sophisticated methods than those used by the Houston Crime Lab, had definitively  “excluded” Mr. Sutton, proving he could not have committed the rape.

“It is gratifying to be able to say ‘I told you so,’ but we need to focus on the underlying problems that led to this false conviction,” said Thompson.  “The error in Sutton’s case is just one indication of serious problems in the HPD crime lab and in the justice system of Harris County, Texas.”   

Thompson began examining the work of the Houston Police Crime Laboratory last Fall at the request of investigative reporters from Houston television station KHOU.  According to KHOU Investigative Producer David Raziq, rumors had circulated for years about bad work by the HPD Crime laboratory.  Raziq and his news team used the state public records act to obtain copies of laboratory records and court documents in a number of cases but needed expert assistance to evaluate them.  “We were told that Thompson is the best person in the country with regard to finding problems in forensic DNA lab work,” said Raziq.  “We were delighted when he agreed to help us.” 

Thompson first spoke out about problems in the HPD Crime Laboratory last Fall after reviewing laboratory work and expert testimony in seven criminal cases.  “It was the worst laboratory work I have seen,” said Thompson.  “The laboratory failed to run essential scientific controls, failed to document their work adequately, and engaged in a variety of practices that create a risk of error.”  To make matters worse, Thompson said, laboratory analysts were reporting their results in a misleading manner in written reports and in courtroom testimony.  “They consistently overstated the statistical significance of their findings,” Thompson said.  Furthermore, Thompson added, “in at least two instances the laboratory reports appeared to be inconsistent with the underlying scientific data.  It appeared that the DNA analysts were stretching and distorting their findings to help get a conviction.”  According to David Raziq, Thompson's criticism backed up allegations of forensic scientist Elizabeth Johnson, a long-time critic of the HPD lab.  Johnson had been raising concerns about the quality of the lab's work for years.  KHOU also consulted several other prominent experts who supported Thompson’s conclusions.

In November, the television station broadcast a series of stories reporting that Thompson and other experts had criticized the HPD laboratory.  The police department responded by asking the Texas Department of Public Safety, the agency that operates the Texas state crime laboratories, to perform an audit of the Houston Police Crime Lab.  An audit report, released in January, confirmed Thompson’s claim that the laboratory was employing dangerous and inappropriate procedures, and led the police department to suspend operation of the DNA/Serology section of the laboratory. 

Currently the district attorney’s office for Harris County, which includes Houston, is reviewing all cases in which DNA evidence contributed to a conviction and plans to have DNA evidence in a number of cases re-tested at independent laboratories.   At a hearing before the Texas state legislature in Austin last Thursday, police officials acknowledged that there have been serious problems with the Houston Police Crime Laboratory for years and promised to bring in an outside panel of experts to help reform laboratory practices.  

In January, Thompson reviewed the DNA evidence in Josiah Sutton’s case.  In that case a woman was abducted at gunpoint and raped by two men.  A week later the woman called police after seeing two men on the street who resembled the rapists.  Based on the woman’s tentative identification, Josiah Sutton and a friend named Gregory Adams were arrested.  The HPD Crime Laboratory tested semen samples collected from the victim and reported finding a mixture of DNA consistent with the DNA profiles of Sutton, the victim, and an unknown second man.  Adams was excluded by the test and was released.  Sutton was brought to trial and convicted based on the victim’s eyewitness testimony and the DNA evidence. 

According to Thompson the HPD laboratory analyst and the prosecutor misrepresented the DNA evidence in several respects.  “The testimony left the impression that the DNA evidence identified Sutton uniquely and definitively as one of the rapists,” said Thompson.  In fact, the tests performed by the laboratory were not definitive.  “If police picked any two black men off the street, the chances that one of them would have a DNA profile that ‘matched’ the semen sample as well as Sutton’s profile is better than one in eight,” said Thompson.

To make matters worse, the laboratory had reported incorrectly that a semen stain found on the back seat of the victim’s automobile, where the rape occurred, contained a mixture of DNA from Sutton, the victim, and an unknown man.  According to Thompson, the laboratory report was wrong.  The semen stain actually appeared to come from a single man.  Based on the DNA profile, that semen donor could have been one of the rapists (the profile was consistent with other samples collected from the victim), but the semen donor could not have been Mr. Sutton. 

While studying the DNA profile of the backseat semen stain, Thompson had a critical realization.  “I suddenly realized that if the stain on the backseat came from one of the two rapists, it was possible to infer the DNA profile of the other rapist.”  Because the DNA of the two rapists was mixed together in vaginal samples collected from the victim, it was unclear which genetic characteristics were associated with which man, making it difficult to narrow the range of possible contributors.  Reasoning logically based on his knowledge of the genetic characteristics involved, Thompson was able to subtract the contribution of the man whose semen was on the backseat, revealing a more complete DNA profile for the other man.  “It was a revelation,” said Thompson.  “It was clear that the profile of the other man did not match Mr. Sutton.”  Hence, if the semen on the backseat came from one of the rapists, then Sutton could not be the other rapist.

When KHOU reported Thompson’s conclusions, the District Attorney’s office agreed to allow additional DNA testing.  A tiny bit of semen that doctors had collected from the victim, immediately after the crime, remained on a microscopic slide.  This sample was tested last week at a private Houston laboratory called Identigene.  Using new test procedures more definitive than those used by the HPD Crime Laboratory, Identigene was able to confirm Thompson’s inference.  The semen contained a mixture of DNA from two men, and neither of those men was Josiah Sutton. 

Sutton’s lawyers are expected to file motions this week asking that he be released immediately from prison.  

Peter Neufeld, who co-directs the Innocence Project at Cardozo Law School in New York, said that there have been 124 previous cases in which DNA testing exonerated a prison inmate.  However, the Sutton case is one of only two cases in which DNA evidence also figured in the false conviction.  Neufeld praised Thompson’s efforts.  “Professor Thompson deserves tremendous credit for exposing this miscarriage of justice.  He has performed an important service to the cause of justice.”  Neufeld noted that the case may also have significance for the debate about the fairness of the death penalty.  "Thompson's work is particularly important because he has identified a crack in the Houston Police Crime Laboratory, which has been the nation's #1 pipeline to execution."

Professor Thompson may be contacted at:

949-824-6156 (university office)

For additional background on this story, see articles in the Houston Chronicle (Jan 31, 2003; March 11, 2003); the New York Times (Feb 9, 2003; March 11, 2003) and at