BLOOD ON CONCRETE

In a previous posting I showed the color change in blood when it dries on a paper towel. In the early phases of making those scans, I was surprised at the sharp increase in color after two hours, and the subsequent almost imperceptible change out to seven days. I considered that a different result might be observed with blood on concrete, found a broken piece of concrete with a troweled surface, and cleaned and dried it. I then tackled the lemon
tree again, and predictably produced another blood sample, which I deposited on the smooth surface of the concrete chunk. As before, I scanned it at intervals, and saved the various scans to separate files; the conditions were as for the blood-on-paper experiment: drying in air at 60 to 70 degrees F and relative humidity of 50% to 75%, out of direct light except during scanning. The same scanner settings were used throughout.

The concrete chunk was put directly on the scanner bed without intervening photography. In the early exposures, a yellow toothpick was used to hold up one edge of the chunk, and thereby avoid transferring blood to the scanner bed. Before the test a one inch long pencil mark was made on the left side of the chunk to serve as a dimensional reference. wpe2.jpg (65074 bytes)

Three different regions are recognized. The entire stain at "A" and the top part of the lower stain are thinner than a drop of blood, and could be described as "smears." The location at the head of the arrowhead, "B" is about the thickness of an isolated blood drop. The stain at "C",bounded by a convex upward curve, is on a nearly vertical surface of the chunk, not in the plane of the troweled surface.

RESULTS: The change in color with time was much different than in the experiment with blood on paper. On concrete, the change is more uniform with time, much slower, and does not show as much total change in color. In particular, my first impression on seeing any of these sample is that they are of blood; I think most people would recognize the red-brownish hue as
characteristic of drying blood.

Even though the samples age much differently on concrete than on paper, the critical conclusion is the same: one can not tell the age of the sample from looking at its color. Compare, for example, the result after 12 hours with that after 7 days. If seen in isolation without the other to compare it with, I would think most people would not be able to judge one as older than the other; I can not. In fact, it is even difficult to distinguish between the
fresh and the 12 hour samples.

So, even though blood changes color differently on concrete than on paper, I would still judge that a person can not tell the difference between "old blood" and fresh blood just by looking at it. But, the samples are there for you to make your own judgment.

SPECULAR "SHINE": During the trial, Fuhrman testified that under the flashlight, the bloodstain on the Rockingham glove showed a "glisten or sheen." The statement has been interpreted as implying a freshness to the sample, and Fuhrman's observation has be derided as being ridiculous. During the blood on paper trials, I looked for a "glistening" in a dim room under a flashlight, and after the first few samples did not see any. I examined the samples on concrete for the same indication, and found a much different result: they appeared to "glisten" all the way through the series -- even out to seven days. The appearance seemed to be as though the samples formed a reflective and relatively permanent "varnish" over the surface. The resulting shininess is not apparent when the source of light is straight on, but becomes conspicuous when the sample is lighted obliquely.

A suggestion of this is seen in the accompanying set of scans from the 12 hour example onward, in the vertical stain at "C". This was lit obliquely by the scanner light source, and regions of white dots can be seen there. Eyeball examination of this effect leads to a description as "glistening." The effect is much more noticeable under the flashlight, however, and is seen on the flat surface very conspicuously.

From this, there are two conclusions. The first is that there does not appear to be any reason to believe that Fuhrman was lying, mistaken, or embellishing. Insofar as blood on concrete shows "glistening" even after 7 days, it is not at all obvious that another surface -- leather -- might not also show glistening a long time after blood is deposited on it. The second conclusion is that we were mistaken to interpret "glistening" as indicating freshness of the stain, since this condition can be seen, under some conditions at least, a week after the blood is deposited. We were led astray because we had not made a methodical study of drying blood. We did not know that the "freshness" indication with which we were most familiar ("glistening" on paper or cloth) does not apply to concrete. And, nobody who did know bothered to tell us.

Were we misled? Of course we were. But, it is not clear that we were lied to. Can a person tell a recent (12 hour old) blood stain on concrete from an old (7 days) stain? No. Some people might be able tell a brand new (less than 2 hours old) stain from one that was a week old, but most of us could not reliably do even that. So, even after the blood-on-concrete test, it appears that a policeman's opinion that he was looking at blood (or a remarkable facsimile) is reliable, but his guess about its age is not. And, we are enlightened about "glistening."



Dick Wagner • Van Nuys, CA (5/31/98) NG212

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