Silent Witness - Volume 4, Number 2, 1998

Maryland's First Mitochondrial DNA Case - The Trial Prosecutors' Experience

by Frank R. Weathersbee, States Attorney for Anne Arundel County, Maryland, and Anne Colt Leitess, Assistant State's Attorney for Anne Arundel County, Maryland

The retrial of the case of Maryland vs. Scotland Williams illustrates that although DNA is a powerful tool, presenting it to a jury can be a complicated endeavor. Defense attorneys can attack DNA so as to confuse, mislead, and weaken the impact of the prosecution’s evidence. The following is an account of our experience in prosecuting this case, as well as some tips that come from surviving weeks of motions, hearings and a trial where the defense had an attorney who specialized in DNA, and two experts who worked closely with the defense attorneys.

In May, 1994, 31-year old Scotland Williams entered the Annapolis, MD weekend retreat of a married couple from Washington, D.C. After robbing the couple of their ATM cards and PIN numbers, Williams handcuffed and shot each of them in the back of the head. Williams was later arrested after he was photographed using the victims’ bank cards at local ATM machines. At the time of his arrest, Williams was in possession of a watch belonging to one of the victims. Further, a shoe print left in the kitchen could also be linked to Williams.

During an investigation of the crime scene, investigators located pubic and head hairs in the victims’ bedroom. The FBI later analyzed these hairs and determined that they were microscopically similar to Williams’ hairs. Further, Williams apparently drank water from a glass in the victim’s home, leaving saliva which contained his epithelial cells.

When the case was first brought to trial in 1994, a private laboratory performed PCR testing on the epithelial cells, and concluded that the probability that they belonged to someone other than Williams was 1 in 890. A jury convicted Williams of the two murders based on this and other evidence, but the case was later overturned on appeal. One of the reasons the appellate court cited was that the trial judge had improperly restricted cross-examination of the prosecution’s DNA expert.

By the time of the 1998 retrial, DNA typing technologies had evolved dramatically. The private lab retested the epithelial cells utilizing a more advanced PCR typing technology and determined that the random match probability was 1 in 3200. Translated into a percentage, that meant that 99.9 percent of the population could be excluded as a source of the DNA on the glass, yet Williams was not. Also, Mitochondrial DNA typing technology had arrived on the forensic scene, enabling the prosecutors to submit the pubic and head hairs to the FBI’s Mitochondrial DNA unit for comparison with Williams’ blood. Prior to the advent of mitochondrial DNA testing, hairs could be subjected to DNA analysis only in cases where the root was still attached.

Found in every human cell, Mitochondrial DNA is more robust than the nuclear DNA used as the basis for other types of DNA testing. Thus, Mitochondrial DNA typing can be performed on evidentiary samples that are severely degraded and extremely old. MtDNA testing can work on hair, bone, teeth, blood, fingernails and saliva. In our case, hairs which had been mounted on slides for several years could still be tested. The FBI’s testing revealed that Williams’ mtDNA type was the same as those in the hairs found in the victims’ bedroom, and that such a type had been observed only the one time in the 319 samples accumulated by the FBI for Williams’ racial group. Williams was, therefore, included as a possible contributor of those hairs.

The Williams case marked the first time that mtDNA was used as evidence and admitted by a Maryland court. The State gained the admission of the mtDNA evidence after an extensive Frye hearing. With the assistance of scientists from the FBI and the Armed Forces DNA Identification Laboratory, the State demonstrated that mtDNA testing had been used for many years in the identification of war casualties, in the study of degenerative diseases, in anthropological studies of man, and in the forensic community as a tool for human identification.

The extent to which we had to familiarize ourselves with the scientific and practical aspects of DNA was a function of the defense put on in the case. Given the outcome of the first trial, the judge presiding over the second trial allowed greater latitude to the defense on the DNA issues in general. From the outset of the retrial, the defense attacked the laboratory that performed the PCR testing and its practices. The laboratory’s record keeping, its procedures, and its reporting of results were all fair game for the defense. The defense’s theory was that the PCR DNA testing and the mtDNA testing was unreliable because of contamination that occurred during the testing process. The defense fought for and won additional discovery in order to show that the laboratory had some instances of contamination which could have affected the testing in the Williams case. The defense was permitted to examine several hundred of the laboratory’s files to check for instances of contamination in other cases. The defense found no other examples of contamination but discovered other issues which they then utilized to criticize the laboratory. The attorneys for the State were familiar with procedures of the laboratory and were able to counter these arguments with the assistance of the State’s expert.

The defense argued that any of the results the laboratory obtained could be caused by contamination and were not the results of the actual sample. Contamination simply means that there is evidence of human DNA appearing somewhere where it is not expected to be seen, such as in a reagent blank or a negative control sample. Contamination does not change one DNA type into another. It merely makes the results inconclusive or reported with caution. The defense, however, argued that because there was faint contamination in two of the twenty items of evidence submitted, the jury should not trust any of the testing. The two items in question were tested at a separate time and place from the crucial evidence and would have had no effect on it.

The defense also argued that the authenticity of the known samples of the victims and the defendant was suspect. Because the defense became so involved in the minutiae of the case, the prosecution had to know enough about the science in order to answer the numerous claims the defense made at both the Frye hearing and the trial. The attorneys for the State visited the laboratory, met with the scientists numerous times, and spent many hours reading transcripts of other hearings and trials involving DNA and this particular set of experts and defense attorney. Without this preparation they would have been unable to anticipate the defense’s attacks on the DNA evidence.

The creativity and the lengths that the defense went to in trying to attack PCR then carried over into their attack on the mtDNA. The defense called two experts who were academics in the field of microbiology. Although neither expert had ever performed this type of testing, or used Sequence Navigator, the software the FBI uses in reading the results, they claimed the FBI did not know what it was doing. The FBI has studied mtDNA for many years, and has validated its procedures and results. Their studies have confirmed that they can assess the level of contamination in a sample, and as long as it is 10% or less of the entire sample, it will have no effect on the results. The defense expert attacked this as bad science and declared that even the slightest contamination renders the results unreliable. The defense experts criticized one of the scientific instruments used by the FBI in mtDNA testing on the grounds that no other laboratory used it. At that time, however, the instrument was very expensive and not many other laboratories were doing mtDNA testing in the United States. The defense experts’ conclusions as to the mtDNA testing were that it would have been impossible to interpret the results as the FBI did and that there was bias and inconsistency in the reported sequencing of the samples. The defense hammered the issue that contamination made the results unreliable and presented huge posters illustrating large peaks of contamination that were seen in one of the samples. Although the posters showed a contamination level under the 10% threshold that would not have affected the results, the visual impact of the posters on the jury was significant.

Dealing with experts who made blanket comments as to the unreliability of the testing in both types of the DNA testing was difficult. When asked by the defense what the expert’s opinion was of the PCR testing, one expert said, “I found the results to be wholly untrustworthy and inconclusive, and the laboratory to be suffering from widespread contamination.” The expert refused to acknowledge that the known blood samples taken from Scotland Williams had the DNA types which were reported as his. He made statements that another person’s DNA could have gone into the tube marked as the reference sample DNA of Scotland Williams. He refused to agree that the laboratory had done anything right. Cross-examining an expert who will not agree on even the slightest finding of the state’s expert was a challenge and made it impossible to validate any of the testing. Convincing a jury to disregard the defense’s assessment of the DNA would be even more difficult.

The end effect on the case was that during deliberations, the foreperson refused to deliberate or look at the over 120 pieces of physical evidence the State had introduced. Her reason was that because the DNA could have been contaminated, she would not give it any weight. Several other jurors were able to convince the foreperson to convict based on the other, non-DNA evidence. The issues of contamination and laboratory procedures were the areas which the defense could attack, regardless of their expert’s credentials. Because DNA is so technical, an attack on appealed to a layperson was an effective defense tactic.

After the verdict, the jurors were eager to talk to the prosecutors. The jurors told the attorneys that several of them had a difficult time with the DNA. According to one of the jurors who later spoke to them privately, those jurors with “follower” type personalities were most easily led astray by the defense. The jurors were split 9 to 3 on the value of the DNA evidence. The contamination issues that were brought up by the defense had an effect on the jurors’ beliefs in the reliability of the evidence. To resolve the impasse, the jurors relied on the non-DNA evidence connecting Williams to the murders. The jurors agreed that much of the evidence presentations were boring. Several jurors, however, also stated that the cross-examination of the defense experts was so effective, that the prosecution was able to make them look like mouthpieces for the defense, and that the experts were discredited in the field of expertise for which they were offered.

In conclusion, the prosecutors thought that the DNA in this case was worthwhile. Although several of the jurors were not convinced by the DNA evidence, the prosecutors believed that it strengthened the rest of the their case. It made the jury’s reliance on the many other circumstantial pieces of evidence that much more credible. DNA was one of the pieces of the puzzle in convicting a killer.

New Guidelines for DNA Forensic Laboratories

As of October 1, 1998, any laboratory performing forensic DNA testing must meet the standards promulgated by the federal DNA Advisory Board in order to receive federal funding, or to participate in CODIS. Created by the DNA Identification Act of 1994, the DNA Advisory Board is made up of scientists and legal scholars who were appointed by the FBI from nominations submitted by the National Academy of Sciences, the American Academy of Forensic Sciences, the American Board of Criminalists, and the American Society of Crime Lab Directors. The aim of the DNA Advisory Board is to ensure quality control and quality assurance in DNA forensic testing laboratories.

Among the mandates of the DNA advisory board are specific degree, experience, and coursework requirements for laboratory technical managers and examiner/analysts; facility set-up requirements; evidence control measures such as retention of evidentiary samples for re-testing and storage methods that minimize degradation. Other requirements include equipment calibration and maintenance standards, administrative and technical reviews of all case files and reports, documentation of the monitoring of the testimony of each examiner, external general proficiency testing and annual audits. More information regarding the DAB’s standards can be found on the Web at www.fbi.gov/lab/report/dnates4.htm.