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And at that point, you may wonder if such a small knife could have caused such a large wound, and common sense might seem to say that should not be. Intellectually you might ask yourself, “How can this two-inch blade make this huge stab wound?”

With knife wound dynamics the biggest issue is getting through the skin. The skin is so elastic that it seems to be the hardest organ to penetrate. Once you break the skin, the amount of force required to make large stab wounds may not be as much as you think it is. The body and organs can be damaged, they just get injured once the skin is broken. You can get a wound of a hellacious depth that does not match the size of the knife in question. This is not even considering the kinds of clothing that people are wearing or what the materials are made from.

That is something that we have to consider when investigating crimes. You can have this huge stab wound, but the knife may not be that large. Or we can have this very lengthy incised slash wound made by a huge knife that got no depth because of the way it was handled and the way the bodies moved during the struggle. Maybe somebody sucked their stomach in as someone tried to stab them. The knife came around in a roundhouse and they sucked in their stomach but still you have this hellacious slash wound that is only an inch deep, but is also eight inches long! Or it can go the other way.

And that is why it is so difficult, so hard to label certain injuries and certain knives and trying to match them because people forget the human dynamic and reality that the person is not laying there on the morgue slab when the slash or stab happened. Everybody was moving; everybody had time and space issues that we have to take into account.

All these other factors are unknown until you start getting witness statements–especially the statements of the people involved. That is always interesting because, of course, there are two survivors in an assault case, so there will be two versions that you can bet will be opposite.

You will have a defendant’s version and you will have a victim’s version. You will have an aggressor’s version. Of the victim and the defendant, which was the aggressor? Taking that into account, you then have to try to figure out how the statements and physical evidence fit together.

If it is a homicide case, you may have one person’s version to analyze, one person’s version out of which to try to make sense. The dead guy is only going to talk as much as the science allows. You are not going to have another verbal story of what happened unless there are witnesses. The dead person is only going to tell us as much as what his body will tell: what the actual wounds, what the actual injuries tell us. He is not going to be able to give us a verbal story of what took place.

eJournal: That puts a lot of reliance on correctly interpreting the scientific evidence, especially if it is not the same as what other witnesses report.

Bunke: Also, the persons involved often are the worst reporters, because of all the physio-psychological effects including tunnel vision, auditory exclusion, distortions in perception of time, or what ever else it may be. We are taking the best witness to the event, who we know is the worst reporter of the event, and trying to extrapolate from their recollections what took place.

eJournal: Does the investigator go into the interview knowing that the witnesses' recollections are going to be diminished by distortions in perceptions?

Bunke: For me, that is very much so. Often times our attorneys don’t quite understand that. They, along with some law enforcement officers and prosecutors, often have a misconception that what they’re being told by the client, by the defendant, by the victim is what actually happened and that their memory is going to be intact and accurate.

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