The wood detective: the cases of the sunken pirate ship, the misunderstood antique, and the wicked pool cue

Science News, Sept 21, 2002 by Susan Milius

Alex Wiedenhoeft has spent the past 7 years answering the same question about 10,000 times. When foresters, lumber dealers, crime investigators, and museum curators really need to know, "What kind of wood is this?" Wiedenhoeft is one of the few people they can go to. "A man called to say he'd bought an end table at an auction for $15,000, which I found flabbergasting just on general principles," remembers Wiedenhoeft of the U.S. Forest Service's Center for Wood Anatomy Research at the Forest Products Laboratory in Madison, Wis.

The caller had thought the table looked European, but after showing it to friends, he had second thoughts. Aspects of the construction seemed early American. If he sent some small samples, would Wiedenhoeft identify the wood and see if that narrowed the possibilities?

Wiedenhoeft studied the samples and reported that they came from one of several kinds of white pine. He stated the limits of his evidence carefully. Yet his report, combined with factors such as the size of the wood pieces and the table's age, suggested that the man had unknowingly bought eastern-white-pine furniture made on this side of the Atlantic. Not exactly bad news: The potential value of the little table, now recognized as a rarity, jumped to more than $100,000.

The 26-year-old Wiedenhoeft represents the new generation of wood anatomists. They're familiar with scanning electron microscopy and molecular genetics. Yet most of the cases Wiedenhoeft gets, even the exotic ones, still depend on spotting classic quirks of wood at the tissue and cellular levels. Optics may have changed somewhat since Sherlock Holmes' day, but Wiedenhoeft still takes his first look at a problem with a handheld magnifying glass.

WOODEN PAST Wood was among the first things that Anton van Leeuwenhoek looked at as he pioneered microscopy in the 17th century. Since then, close study has revealed that tree trunks are great columns of plumbing. Strings of hollow, dead cells--bundled into a massive structure called xylem--carry water from the roots upward to thirsty leaves. Counterpart pipelines of living cells, or phloem, carry liquids the other way, bringing the sugary harvest of photosynthesis from the leaves down to feed the rest of the plant. Generally, outer hark and a layer of phloem surround the thicker xylem, which makes up the wood. Trees tend to deploy several forms of xylem cells in distinctive patterns, so wood anatomists can often narrow tree identification to a group of species.

Much as the O.J. Simpson trial popularized the concept of human-DNA fingerprinting, the sensational 1935 trial of a man accused of kidnapping Charles Lindbergh's baby showcased the power of wood analysis. When Lindberg's 2-year-old son disappeared in 1932, the kidnapper left behind a broken, homemade ladder. During the 2 years that investigators struggled without finding a plausible suspect, that ladder came to represent what little hope there was of cracking the case. Arthur Koehler, one of Wiedenhoeft's predecessors at the wood-research center, worked with police to identify the wood, picking out distinctive marks left by a flawed blade at a sawmill.

Police found their suspect, Bruno Hauptmann, by wood-free means: He tried to spend some of the ransom money. Yet wood had a role in the trial when prosecutors charged that a board incorporated into the ladder had been torn from Hauptmann's house and matched boards still in place there. Koehler testified at what was described as "the trial of the century." To the end, Hauptmann insisted on his innocence. He was a carpenter, he said, and if he'd made the ladder, it wouldn't have broken. Nevertheless, he was convicted and electrocuted.

In more recent years, forensic botany has lagged behind other biological disciplines in crime fighting, laments Jane Brock of the University of Colorado in Boulder. "You can go to any forensic lab, and you can find experts in forensic entomology," she says. Yet she doesn't find in-house botanists.

She's a plant anatomist and has worked with investigators several dozen times, identifying food in victims' stomachs and intestines. Plant cell walls survive digestion in better shape than animal cells do, she says. At the 2002 meeting of the Botanical Society of America in Madison, she convened a special session to encourage academic botanists to offer their expertise to crime fighters. Most current work for wood identifiers lies in commercial disputes rather than in criminal cases, says Wiedenhoeft.

WOOD EYE? To identify wood, Wiedenhoeft says he can deal with samples as small as half the size of a kitchen match. In exceptional cases, he's made do with splinters, though he does not speak of them fondly. The smallest ones he's ever managed to identify were samples that a curator had taken from Italian wood sculptures at the Metropolitan Museum of Art in New York.

As an example of his technique, Wiedenhoeft describes working with a Texas crime lab last year in studying a splintered pool cue that had been used on someone's skull. The lab shipped samples of the murder weapon--"from the nonbusiness end, so it wasn't gory," says Wiedenhoeft--as well as wood slivers recovered from a suspect's car.