In this crime story, the smoking gun was a syringe loaded with sundry viral DNA fragments. It was drawn in a blood sample from an HIV-infected donor patient and injected intramuscularly into the criminal's victim, a nurse he had long been dating. This perpetrator was a gastroenterologist named Richard Schmidt, who practiced in the small city of Lafayette, La., some 100 miles due west of New Orleans.

"It was a 10-year affair," recalled molecular and human geneticist Michael Metzker, an expert witness at the trial. "He was supposedly a very jealous and possessional man. She wanted out of the relationship, and Dr. Schmidt was quoted as telling her, If I can't have you, I'll fix it so nobody will.'"

Metzker, a professor of molecular and human genetics at Baylor College of Medicine in Houston, is senior author of a report in the Proceedings of the National Academy of Sciences (PNAS), released online Oct. 8, 2002.

Its cryptic title: "Molecular evidence of HIV-1 transmission in a criminal case."

"The finding," he told BioWorld Today, "was that we found two individuals - Schmidt's patient and his victim - whose blood contained HIV sequences that were more closely related than any other sequences compared in our study. I wouldn't say that what we actually did was novel," Metzker continued. "The novelty is that this is the first application in a criminal court setting based on phylogenetic analysis. This is a generally accepted method for analysis of relatedness of HIV DNA sequences.

"The crime took place on Aug. 4, 1994," Metzker said. "It happened that I was on a list of names generated by the assistant district attorney in Lafayette. I said there was a test that could address the question of identifying relatedness between individuals and agreed to take on the study. We were involved in the scientific analysis," he went on. "Our investigation first identified the patient under the care of this physician. Also, we followed up all contacts with the victim and tested prior to the time we received their two blood samples. Thus, there was some epidemiological evidence, looking at alternative possibilities for patient-to-victim transmission of HIV. From 1984 to 1995, the victim reported having seven sexual contacts, including the doctor, all of whom were negative for HIV-1."

Cast Of Characters: Criminal, Patient, Victim

He continued: "Once we had identified the patient - a homosexual male infected with HIV in 1990 - two blood draws, one from the patient, one from the victim, were received by Baylor. Then we obtained HIV DNA sequences from both samples. The HIV genome is about 10,000 base pairs in length. We looked at two different gene fragments, a part of the envelope glycoprotein 120 (gp120) and also part of the reverse transcriptase (RT) gene. For testing those two fragments, we obtained 28 local control individuals - all HIV-positive - and compared them by phylogenetics to determine how significant the relatedness was.

"By that method we performed many replicates to take the findings beyond the standard and go to the extreme in sampling to determine how related they were. We converted those into what is known in science as statistical p' values - measures of probability. It was hard for us to equate beyond a reasonable doubt' what we mean from a scientific standpoint. So we used as accurate p' values as possible as a way of equating that in a criminal court setting. Our finding was that, based on the phylogenetic analysis, we found that those two individuals contain HIV sequences that were more closely related than any other sequences compared in our study.

"The basis of phylogenetics," Metzker explained, "is DNA sequencing. So we obtained blood from each individual, extracted genomic DNA, then directly sequenced PCR targeted for the two genes. HIV is a population of viruses. There could be a lot of diverse polymorphisms, insertions and deletions in a sample. We also took that PCR product and cloned it. For the patient and the victim we picked 50 clones from the gp120 region and sequenced every individual clone, then aligned those sequences in multiple alignment. That alignment of nucleotides is the basis for then building the phylogenetic trees. It's really based on the genetics."

Courtroom Drama Ends In Highest Court

"There were five expert forensic witnesses in total," Metzker recounted. "Three on the prosecution side, myself and two PNAS co-authors. The two defense attorneys on the opposing side argued that the relatedness could have been by chance. The verdict in the state of Louisiana court found Dr. Schmidt guilty of attempted second-degree murder. He was subsequently sentenced to 50 years in jail, and is currently serving out his sentence. That was appealed at the state level, leading to an appeal to the U. S. Supreme Court earlier this year. The higher court simply refused the appeal and upheld the state's verdict. Once that was done, we felt that we could appropriately go ahead and publish our study.

"The last I heard about the victim's status is that she is more affected by the hepatitis C virus infection than the HIV. It was a mixture of two blood samples from the two different patients who were under Dr. Schmidt's care."