The Chemistry of Murder

by Deborah Blum

Just for the moment, consider yourself a forensic scientist, an investigator summoned by the police to the scene of a rather puzzling death.

The scene in question is a small, rather shabby apartment in which there has clearly been a gas leak. The cops have opened all the windows to air the place out. In the bedroom at the rear of the dwelling you find a young woman who has clearly been dead for several hours. She lies on the bed - pale, cold and stiff.

Immediately, you realize that something is very wrong with this picture. You have the body sent back to the city morgue for blood tests. And those tests confirm your initial suspicion - the woman did not die of carbon monoxide poisoning.

In fact, further investigation finds that she was suffocated with a pillow before the gas came spilling into the apartment. The killer set the scene hoping that the police would believe it was an accidental death.

So what was the giveaway clue? What made you suspicious when you surveyed that sad little scene?

In fact, this one has an easy answer. If the woman had died of carbon monoxide poisoning, she would not have been pale. Her skin would have been flushed pink; people have actually been known to comment on the healthy look of corpses after a carbon monoxide killing.

There's a very straightforward chemistry to this. When we breathe life-giving oxygen rich air, the oxygen attaches to proteins in blood that carry the gas to every cell in our body. But carbon monoxide (a simple mixture of one carbon atom to every one oxygen atom) bonds much more efficiently to those proteins. I tend to think of it as a chemical thug. It muscles oxygen out of the way, grabs onto the carrier proteins (hemoglobins) and rapidly saturates the blood. That means that even if you are breathing air with some oxygen in it, the carbon monoxide crowds it out.

When enough carbon monoxide invades the blood stream, people die - usually a saturation above 50 percent although some people have been killed by levels in the 40 percent range. Carbon monoxide is a byproduct of the burning of fossil fuels - from gas for lighting, to natural gas for heating, to gasoline in automobiles - and it is an exceptionally efficient killer; in a closed garage, for instance, with a car left running, it has been known to kill people in as little as ten minutes. An analysis by the U.S. Centers for Disease Control estimated that about 500 people in the United States die from carbon monoxide poisoning every year and 15,000 require emergency treatment for exposure to the gas.

These poisonings leave visible evidence behind. As carbon monoxide levels rise, it sets off a reaction that turns the blood a deep cherry-red, a rosy chemical pink. Even the internal organs gain a dark cherry appearance, easily visible on autopsy. If a body is found pale and cold, many things could be responsible for that death - but definitely not carbon monoxide.

The crime scene I described above actually comes from a murder case in my book, The Poisoner's Handbook, and occurred in 1923. Further investigation found that the dead woman's husband had taken out an insurance policy on her life, suffocated her with a pillow, and then - this is the 1920s, when gas lighting is still prevalent - snapped a gas fitting on a lamp in the bedroom and let the illuminating gas flow out, assuming that police would be fooled.

When pathologists took a closer look at the body, they discovered that he had held the pillow so tightly against her that he had left bruises on the back of her head. When the full chemistry workup was done, the scientists found merely normal urban levels of carbon monoxide in the blood - nothing close to lethal at all.

The husband went to prison and in this case it would be you, the good forensic scientist, who put him there. If someone tried this today - using, say, a "leaky" gas generator instead of old-fashioned illuminating gas - they too would get caught. They too would go to jail. Because a little chemistry - even as simple a calculation as this - goes a long way in catching a killer.

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