Dirty Detecting
Detective novels are my favorite escape reading; I love whodunits and howdidits. Thus I was easily lured into a recent set of articles in the British journal New Scientist that dealt with using science to solve crimes. Among them was a tidy detective story.
It began with an importer in Argentina ordering computers from a manufacturer in Texas. Nowadays money moves electronically, but goods still need physical transport. So the manufacturer packed up the computers and shipped them off--or at least so he claimed when the outraged Argentinean reported that the boxes he received contained only concrete blocks.
Whodunit? The computers could have been swapped for concrete blocks at either end of the transaction or many places in between. There were customs brokers, airports, warehouses, all manner of opportunities during transit for the light-fingered and immoral to make a switch.
Appropriately for solving a commercial crime, the investigation involved a commercial evidence analyst. Skip Patenik, who operates out of Elgin, Illinois, is one of the world's experts in the minute clues that constitute trace evidence. Patenik employs an array of high-tech microscopes in his work, and has enormous files of reference materials--not books and article reprints as academic scientists might have, but real materials: pollens, fibers, soils, paints, and other items for comparison in identifying traces left at the scene of a crime.
In the concrete computer caper, finding the scene of the crime was Patenik's assignment. Once that location was known, the proper authorities could carry out the on-site investigation.
To pick the spot, Patenik in effect took the concrete's fingerprints. Concrete is a mix of cement and aggregate, which is sand or gravel of an appropriate type for the concrete's intended use. The aggregate usually comes from a source near where the concrete is made. In this instance, that might well be close to the scene of the crime. So Patenik concentrated on the aggregate.
It was sand, and the sand grains were all nearly the same size. Beach sand has that characteristic, because wave action tends to sort the grains by size. Scanned by electron microscope, the sand grains revealed another significant characteristic: their surfaces were gouged with tiny triangular pockmarks. Such marks develop when waves bash the sharp edge of one sand grain into the smooth face of another.
Taken together, those features indicated that the concrete came from a coast, but picking which coast demanded other sorts of research. First, chemical analyses showed that each sand grain had a particular mix of heavy minerals. Then came a review of oil company records, particularly those from the 1930s and 1940s. During those decades the companies funded many studies of the heavy-mineral content of rocks and sands, believing these minerals might hint at underlying petroleum. Pursuing that paper trail, Patenik found a close match for his sand, in southern Florida. The computer shipment had been sent via Miami; the police now had a much warmer trail.
Near the Miami airport, they soon found a pile of concrete blocks identical to the ones that had replaced the computers. That vital clue led eventually to the identification and arrest of the thieves.
Could Alaska thieves be caught by similar evidence? I called the state Division of Geological and Geophysical Surveys.
The answer: probably not. Because Alaska is so huge, the data about all manner of dirt, from deep boreholes to shallow borrow pits, is very patchy. Unless the aggregate came from some very well studied place--say downtown Anchorage--concrete blocks made here probably wouldn't point to the thieves.
But the home team has its own crime-fighting abilities. A few years ago, a DGGS geologist helped solve a case involving stolen placer gold. Placer gold has its own fingerprint. The geologist analyzed the size and configuration of the placer grains in the accused thief's possession, and showed that they had come from the mine where the theft occurred.
