Ed. Note: Chris Halkides has been kind enough to try to make us lawyers smarter by dumbing down science enough that we have a small chance of understanding how it’s being used to wrongfully convict and, in some cases, execute defendants. Chris graduated from the University of Wisconsin-Madison with a Ph.D. in biochemistry, and teaches biochemistry, organic chemistry, and forensic chemistry at the University of North Carolina, Wilmington.
Patricia Stallings took her infant son Ryan to the hospital because of lethargy, vomiting and other symptoms. The hospital tested Ryan’s blood and found what it believed to be evidence of ethylene glycol and metabolic acidosis (his blood was too acidic). The key ingredient of antifreeze, ethylene glycol, produces low pH and can be fatal when it is ingested and metabolized into oxalate, which forms crystals with calcium ion in the brain and kidneys.
Ryan was released into foster care, and Patricia and her husband were allowed weekly visits. Ryan became ill after one of these visits and, about four days later, he died. His blood pH was even lower than after the first episode and the level of ethylene glycol was even higher, about 900 milligrams per liter.
Patricia Stallings was arrested and placed into custody. The main evidence against her was that two labs had claimed to find evidence of ethylene glycol (some antifreeze was found at their home). She was subsequently convicted of murder and sentenced to life without parole.
Patricia Stallings was already pregnant with another son, David, at the time of her arrest. After David was born, he was cared for by others, yet he began to show similar symptoms. Eventually he was diagnosed with methylmalonic acidemia (MMA). MMA is caused by a failure of an enzyme to work properly, leading to a build-up of compounds including methylmalonic acid and propionic acid in the blood and urine. MMA is a rare genetic disease, but the fact that David suffered from it indicated that Ryan had a one-in-four chance of having it as well.
Although this diagnosis was known by the start of Patricia Stallings’ trial, the judge prevented her attorney from presenting this theory to the jury. The defense attorney later said that he might not have understood exactly what he needed to do in order to get the judge to allow him to make this argument.
To understand what went wrong in this case, one must have some knowledge of clinical chemistry. Gas chromatography (GC) is a technique in which substances pass through a column of a waxy liquid based upon their chemical properties. The period it takes to emerge is the retention time. Different substances ordinarily have different retention times, but any two substances may have the same retention time within experimental error. GC is the technique that the two labs used to identify ethylene glycol. The first lab claimed it had identified ethylene glycol despite an apparent discrepancy in the retention times between the unknown substance in Ryan’s blood and standard of ethylene glycol, and the second lab did not run a standard at all.
Although it can be used to find the quantity of a substance, GC gives only one piece of information that bears on the identity of that substance, the retention time. Mass spectrometry (MS) gives the mass of molecule and usually provides additional information, based upon the mass of fragments of the molecule. Gas chromatography and mass spectrometry (GC/MS) are particularly powerful when they are coupled; gas chromatography separates mixtures, often into pure molecules, and the combination of retention time and the mass of the molecule and its fragments identifies it.
Dr. James Shoemaker’s initial finding of methylmalonic acid in a sample of Ryan’s urine suggested that he also suffered from MMA, and this information was given to the District Attorney and through that office to Patricia Stallings’ lawyer. But the lawyer did not fully appreciate the information.
A biochemist, William Sly, and the man who later became Patricia Stallings’ lawyer, Robert Ritter, independently saw an episode of the television program Unsolved Mysteries about the Stallings case. Mr. Ritter visited Mrs. Stallings in custody and became convinced of her innocence. Professor Sly and a geneticist Piero Rinaldo continued to examine the case, along with Dr. Shoemaker.
Their tests, performed under essentially identical conditions to that employed by one of the labs, showed that ethylene glycol and propionic acid standards emerged from the column with similar but distinct retention times. When a sample of Ryan’s blood was spiked with an internal standard of ethylene glycol, it was unequivocally a distinct substance from the unknown compound, which was shown to be propionic acid by GC/MS. Clearly Ryan also suffered from methylmalonic acidemia. The prosecutor acknowledged that Patricia Stallings’ first lawyer had been ineffective, and she was granted a new trial. Several months later, the prosecutor’s office dismissed all charges.
One of the most important factors in this wrongful conviction was expectation bias. This caused the first lab to brush off the mismatch between standard and control and caused the second lab to assert a conclusion not based on evidence. Moreover, MMA is a rare disease; Bob Mead implied that if the doctors treating Ryan were more familiar with ethylene glycol poisoning than genetic diseases, it might have colored their interpretation. Indeed, when samples of serum spiked with propionic was sent to three labs, two of the three misidentified the substance as ethylene glycol.
Another key factor was uncritical reliance on a chemical technique that provided limited information. Bob Mead also highlighted the potential contrary information that was ignored: Ryan would have had to consume 300 liters of ethylene glycol to account for the amount of unknown substance found after the second episode (ethylene glycol is rapidly excreted from the body, and about 100 hours elapsed between Patricia’s visit and the test). The innocent presence of antifreeze in the Stallings’ garage was interpreted as evidence of guilt.
With respect to this case, Judge Rick Teitelman said, “I don’t think there is another lawyer in America who could have done what Bob Ritter did.” Clearly Drs. Shoemaker, Sly, and Rinaldo (who was refreshingly blunt about the poor quality of the initial laboratory work) deserve considerable credit for engaging with the legal system. Prosecutor George McElroy III behaved in a reasonable fashion. But there were also elements of chance: David Stallings’ being born with the same metabolic error and that two of the principals happened to independently watch an episode of a television show.
Conger Beasley, Jr., “The Right Man for the Job” Missouri & Kansas Super Lawyers, November 2007.
Bob Mead, “Accused and Convicted—a case study” Proceedings of the Royal Society of Western Australia July 2007.
James Shoemaker, Robert Lynch, Joseph Hoffman, and William Sly, “Misidentification of propionic acid as ethylene glycol in a patient with methylmalonic acidemia,” Journal of Pediatrics 1992, 120:417-421.
Bill Smith, “Not Guilty: How the system failed Patricia Stallings” St. Louis Post-Dispatch