TOLEDO -- Detectives say they used what is called blood transfer evidence to help identify a suspect in the 24 year old murder case of Sister Margaret Ann Pahl.
The 1980 murder of Sister Pahl was reopened after detectives conducted what is called blood pattern analysis. Sgt. Steve Forrester said, "This is actually when a weapon is laid down or anything is laid down, it leaves a pattern. So we're talking about blood transfer patterns as opposed to DNA evidence when we talk about the technology."
Professor Herbert MacDonell, from Corning New York, is an international expert in this field. He founded the Bloodstain Evidence Institute in 1973. Over the years he's taught thousands of detectives, forensic scientists and attorneys what to look for. "We teach them the laws of physics of blood stain pattern formation. You may call it hydrodynamics," said Macdonell.
Macdonell uses geometry to figure out how a crime is committed and how blood is transferred. Sometimes it's a compression transfer, other times there can be a smearing of blood. So how accurate is it? "The accuracy of a blood stain pattern interpretation is based on the knowledge of the person that is making the analysis," said MacDonell. He finds it to be very accurate if used properly, although results can sometimes be subjective. "It means if you and I look at something. You may have one conclusion and I may have another and the one who is more experienced will usually be more accurate," said MacDonell.
MacDonell says blood pattern analysis is accurate years later as long as evidence is preserved and there are good photographs. But as an expert witness, he knows there's no guarantee a jury will see things the same way scientists do. "You can lead a truth to a jury, but you can't make them believe it. Sometimes they can come to the right conclusion for the wrong reason, in my opinion based upon the evidence," MacDonell.
MacDonell says blood transfer pattern analysis has been around since the late 1880's, even though many people aren't familiar with it.
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