Expert Witness: Methane & Manslaughter

The Statue of JusticeAs a chemist, I’ve been involved in many projects for a variety of clients for lots of different reasons. Sometimes, I use analytical chemistry, the scientific method, and my skills to assist a jury in reaching a legal conclusion. Often, these cases are about patent infringement, misappropriation of intellectual property (my non-legal translation is “stealing company secrets”), or product defects. From time to time, however, I’m asked to serve as counsel for cases in which a manufactured product is claimed to be the cause of a death or injury. These situations are highly unfortunate and can require detailed analysis to understand the probable root cause.

A particularly unusual case involved an investigation into a 92-year-old man’s cause of death. “Methane,” the predominant component of natural gas, was the listed cause of death. The allegedly responsible party accused of manslaughterer was the furnace repairman.

The elderly man was discovered by his daughter in the bedroom, which doubled as the furnace room. Shortly before his death, the natural gas furnace had been serviced by a certified repairman. The daughter claimed that a faulty repair to the furnace flue created a gas leak, thereby causing her father’s death.

The sole piece of physical evidence against the repairman was the coroner’s report, which included the gas chromatography results. The gas chromatography results seemed to corroborate the daughter’s claim.  Several days post-mortem, the coroner used a gas-tight syringe to acquire a sample from the decedent’s lungs. The results included the chromatogram and a data table identifying each chemical that was present in the lungs. This coroner’s report supported the allegation that the inhalation of methane was the cause of death.

The defense attorneys hired me to evaluate the coroner’s report, advise them about the relevant science, and develop an explanation that would be fully understood by a jury composed of people with a variety of educational backgrounds.

The Rebuttal Process

Serving as an expert witness is an interesting and challenging opportunity to use education, training, and experience to offer opinions to a judge and jury. No other person can offer opinions in a trial although some people can provide testimony as fact witnesses. My specific role in this case was to objectively scrutinize the coroner’s report and to make a determination as to what the report really indicated. Here’s how I did that.

If you’ve watched “CSI:Miami”–or any “CSI” show, for that matter– you’ve never heard the detectives request a GC-TCD test: Gas Chromatography- Thermal Conductivity Detector. The GC-TCD is capable of separating a mixture of volatile chemicals, like those present in the man’s lungs. This type of detector is considered to be “non-selective” because it simply responds to the presence of any chemical in the purge gas if that chemical has a thermal conductivity value that is different from the purge gas’s value. Specific chemicals will cause a peak in a predictable position on a plotted chart. Here’s a nice bit of foreshadowing (just like in the TV shows): different chemicals can occupy the same position on the chart.  

So, instead of a GC-TCD, nearly every crime show (if not all of them) uses “the GC Mass Spec” to solve a case. What’s the big deal with GC Mass Spec? The mass spec (the full name is mass spectrometer ) is a selective or “smart” detector. In contrast to the TCD, the mass spec can provide the exact identification of each separated chemical.

In our “not-CSI-and-not-television-magic” scenario, the corner used a GC-TCD. Using this selection of gas chromatography as an analysis method wasn’t the problem; the coroner was able to determine that the lung sample contained several components and was able to say that one of the peaks occurred in a position on the plotted chart that was consistent with methane. However, other chemicals can potentially occupy that same position on the chart. With the single GC-TCD result the coroner could not prove that methane was present. Rather, he could only conclude, scientifically, that methane may have been present in the lung sample (See? I told you that would be important).

If the coroner had used the GC mass spec method, a mass spectrum that is unique to methane would have been obtained if methane was present in the sample. The highly definitive ability of GC mass spec is why 1) it’s used almost exclusively in CSI shows (unless they’re looking for a plot twist), and 2) it’s the method that modern juries fully expect to be used for cases involving chemical analysis.

Furthering our defense, the coroner also didn’t include an evaluation of the methane concentration claimed to be present. This was particularly troublesome for the plaintiffs for at least two reasons. First, a careful analysis of the composition of “everyday air” should always detect methane, because methane is a trace component of the atmosphere. Secondly, any analysis of the decedent’s respiratory tract should detect methane, because decomposing organic material produces methane gas.

Presentation to the Jury

Unlike in CSI, where the testimonies are often dramatic and underscored by an intense soundtrack, real-life testimony for us is, in large part, teaching. Complex topics need to be presented quickly and clearly to a jury of people with different education levels, backgrounds, and very broad levels of engagement in the jury process itself. I needed to make gas chromatography understandable to a jury, in such a way that my explanation would be useful.

I started with the basic operating principles of gas chromatography. Then, I described the difference between a non-specific TCD and a “smart” mass spec detector. I introduced the concept of a “chemical fingerprint”: the highly detailed chemical identification provided by the mass spectrometer. Thanks to CSI, jury members seemed comfortable with the role of GC mass spec in investigations.

I explained to the jury why the coroner may have detected methane in the lung sample, but did not prove he really had detected methane with the evidence provided. This fact alone may have been enough to aid the jury in their decision. However, the hypothesis that methane may have been present in the man’s lungs was also acknowledged during the testimony. It was the lack of concentration data which made the report insufficient evidence.

The coroner commented on neither the existence of methane in the Earth’s atmosphere, nor that a decedent’s respiratory tract accumulates methane during the decomposition process. In layman’s terms: the mic was dropped.

The Verdict

And now, the most exciting part of any crime show: the verdict.

Manslaughter case jurors are instructed that guilt must be beyond a reasonable doubt. The way in which the coroner conducted the GC test left a reasonable doubt as to the reliability and relevance of those tests. The furnace (and therefore the repairman) were found “not guilty”. It’s always a great day when we can use our knowledge and experience to help others and speak truth. An added bonus, moving forward the jury could watch CSI with more knowledge, insight, and intrigue than they could have previously.