DNA testing
On the night of 12 June 1994, Nicole Brown Simpson and Ronald Goldman were found brutally murdered at Ms. Simpson’s home. A few days later Ms. Simpson’s ex-husband, Orenthal James (O.J.) Simpson, was picked up by Los Angeles police offi cers and became the chief suspect in the murder investigation. Due to O.J. Simpson’s successful football career and popularity, the case immediately drew the public’s attention. Over 100 pieces of biological evidence were gathered from the crime scene consisting primarily of blood droplets and stains. DNA samples were sent to three laboratories for testing. Over the summer months of 1994, the Los Angeles Police Department (LAPD) DNA Laboratory, the California Department of Justice (CA DOJ) DNA Laboratory in Berkeley, and a private contract laboratory from Maryland named Cellmark Diagnostics performed the DNA testing using both RFLP and PCR techniques. A number of RFLP and PCR markers were examined in this high-profi le case. However, no STRs were typed. The so-called ‘ Trial of the Century, ’ People of the State of California v. Orenthal James Simpson , began in the fall of 1994. O.J. Simpson hired a legal ‘ dream team, ’which worked hard to acquit their client. O.J.’s defense team knew that the DNA evidence was the most powerful thing going against the football star and vigorously attacked the collection of the biological material from the crime scene. Through accusations of improper sample collection and handling as well as police conspiracies and laboratory contamination, the defense team managed to introduce a degree of ‘ reasonable doubt. ’After a lengthy and exhausting trial, the jury acquitted O.J. Simpson on 3 October 1995. Sevensets of bloodstains were collected by the LAPD and analyzed by the three DNA laboratories mentioned above. These sets of samples are reviewed below along with the challenges put forward by the defense team. For each sample, the statistics for the odds of a random match ranged from 1 in 40 when only PCR testing with the DQ-alpha marker was evaluated to more than 1 in 40 billion when all RFLP markers were examined. To gain a better understanding of the magnitude of the DNA testing conducted in the O.J. Simpson case, 61 items of evidence were received by CA DOJ from LAPD (Sims et al., 1995). From these evidence items, 108 samples were extracted in 22 sets and tested alongside 21 quality control samples that were coextracted and 24 extraction reagent blanks. These extraction reagent blanks were performed to verify that no contamination was introduced in the CA DOJ laboratory. Froma scientifi c point of view, the results from the three testing laboratories agreed and more than a score of DNA markers were examined with no exclusions between the crime scene samples and Mr. Simpson. The acquittal verdict goes to show that DNA evidence is not always understood and can be quite complex to explain to the general public. Expert witnesses have the challenge of presenting the diffi – cult subjects of DNA biology, technology, and genetics, and jury members must make sense of concepts such as contamination and mixture analysis that can be fairly complex. To their credit, the defense team focused on the evidence collection and preservation as the most important issues in the trial rather than attacking the validity of DNA testing. They implicated the LAPD in planting some of O.J. Simpson’s liquid blood reference sample collected on 13 June — the day after the murders took place. Furthermore, the defense attacked the manner in which the evidence was handled in the LAPD DNA laboratory and alleged that contamination of the evidence samples by O.J.’s reference blood sample resulted from sloppy work and failure to maintain sterile conditions in the laboratory. The contamination allegation became the focus of their arguments because much of the evidence had been handled, opened, and supposedly contaminated in the LAPD lab before it was packed up and sent to other laboratories for further testing. Thus, according to the defense, no matter how carefully the samples were handled by the California Department of Justice DNA Laboratory or Cellmark Diagnostics, their testing results would not refl ect the actual evidence from the crime scene. Since the samples were supposedly tainted by the LAPD laboratory, the defense argued that the evidence should not be considered conclusive. However, the sheer number of DNA samples that typed to O.J. makes it hard to believe that some random laboratory error made it possible to obtain such overwhelmingly incriminating results. Sincethe conclusion of the O.J. Simpson trial in 1995, forensic DNA laboratories have improved their vigilance in conducting DNA evidence collection and performing the testing in a manner that is above reproach. Because PCR is an extremely sensitive technology, laboratories practicing the technique need to take extraordinary measures to prevent contamination in the laboratory. Hence, the value of laboratory accreditation and routine profi ciency tests to verify that a laboratory is conducting its investigations in a proper and professional manner is clear (see Chapter 13) . Theissuance of the DNA Advisory Board (DAB) Quality Assurance Standards (see Chapter 13) has helped raise the professional status of forensic DNA testing. It is noteworthy that in a systematic analysis of circumstances normally encountered during casework, no PCR contamination was ever noted according to a 1999 study (Scherczinger et al., 1999). Signifi cant contamination occurred only with gross deviations from basic preventive protocols, such as those outlined in the DAB Standards, and could not be generated by simple acts of carelessness. Arguably the most important outcome of the O.J. Simpson trial was the renewed emphasis placed on DNA evidence collection.
Sources:
Levy , H. ( 1996 ) . O.J. Simpson: What the blood really showed . In H. Levy (Ed.), And the blood cried out (pp. 157 – 188 ) . New York : Basic Books . Scherczinger , C. A. , et al. ( 1999 ) . A systematic analysis of PCR contamination . Journal of Forensic Sciences , 44 ( 5 ) , 1042 – 1045 . Sims , G. , et al. ( 1995 ) . The analysis of serological evidence by the California Department of Justice DNA Laboratory in the case of People v. Simpson . In: Proceedings of the sixth international symposium on human identifi cation . Madison, WI : Promega Corporation (pp. 116 – 117 ) . Weir , B. S. ( 1995 ) . DNA statistics in the Simpson matter . Nature Genetics , 11 , 365 – 368 .