Tuesday, May 29, 2012

The Case of Preston Hughes III: On Being Blunt

The autopsy reports for Shandra Charles and Marcell Taylor are quite specific: none of the stab wounds showed a blunt edge. So that you understand what a blunt edge stab wound looks like, I offer the following image from Sharp Edged and Pointed Instrument Injuries, by Dr. William A. Cox.

Image Removed
at Owner's Request

Dr. Cox provided the following caption and credit for that image:
Re-approximation of the wound edges of the above image. Such re-approximation allows one to determine the upper angle is blunt, whereas the lower has an acute angle consistent with a single-edged instrument. (Sharp Force Injuries, J. Prahlow, MD, and S. Cina, MD, Medscape, Mar 29, 2010)
With respect to Brain Teaser #2, Reader Paul was the first to note (via the comments) that the autopsy reports exclude Preston's knife as the murder weapon, since his knife had a blunt edge and their wounds did not. To help you visualize that point, I present once again images of Preston's knife, Shandra's two stab wounds, and one of Marcell's stab wounds.

Preston Hughes' Knife

Shandra's Neck Wound

Shandra's Chest Wound

Marcell's Chest Wounds (Stab upper, cut lower)
I do not have an image of the stab wound to Marcell's neck. Be aware, however that Assistant Medical Examiner Vladimir M. Parungao, M.D., declared that each of Shandra's two stab wounds and each of Marcell's two stab wounds had no blunt edge.

Despite Reader Paul's timely and accurate observation that Marcell's knife could not have created any of the stab wounds found on Shandra or Marcell, I awarded him only 10 of the possible 20 points. I cautioned him that there were two exceptions to be considered, two conditions under which a blunt edge knife might not leave a blunt edge wound. I withheld the remaining 10 points to the first person to describe those exceptions and explain why they do not apply to this case. I guess I will have to award those points to myself.

I return to Dr. Cox for clarification.
One of the most significant determinations that must be made, along with width, thickness and length of the blade, is whether the blade was single- or double-edged or serrated. If the victim has been stabbed with a single edge blade, they will have an acute angle at one end of the stab wound, with the other end being blunted or squared off. 
However, it is well know that stab wounds produced by single-edged blades often have acute angles at both ends. How a single edged blade can produce acute angles at both ends is believed to occur for two reasons.
I'll address the second exception first, and the first second.
The second reason why a single-edged blade can produce acute angles at both ends is because many single-edged blades have a cutting edge on the back of the knife (non-cutting edge) at its tip.
That hardly counts. Dr. Cox explained the obvious, that some blades are actually double-edged near the tip and single-edged near the handle. If only the double-edge portion is inserted, then a blunt end wound would not be expected. I consider the second exception to be the "Duh" exception. Now onward to the first exception.
The first is that the initial penetration by the point of the knife creates a defect with an acute angle at both ends. As the blade of the knife creates a defect with an acute angle at both ends. As the blade of the knife continues to proceed deeper into the tissues, that edge of the defect in contact with the cutting-edge obviously remains at an acute angle. However, the opposite end of the defect, which is in contact with the non-cutting surface does not impart its shape to that end of the skin defect. All the non-cutting edge does as the blade is plunged deeper into the defect is to tear the skin and underlying tissue along the original acute angle. Where this changes is, if the stab wound runs parallel to Langer's lines, than [sic] one end will have an acute angle and the other will be blunted or squared off. In this particular case the width of the of the blunt end of the stab wound will represent to a substantive degree the width of the non-cutting edge of the knife.
Prior to reading Cox, the only Langer's lines I was familiar with were the lines of people waiting to get into  Langer's Deli, home of the best pastrami sandwiches in the world.

Dr. Cox, however, was speaking of these Langer's lines:

I guess I should first mention the obvious. That guy has a few more lines than the guys who posed for the ancient Greek, Roman, and Renaissance statues. Consider, for example, the David guy who posed for Michelangelo.

Now that I don't feel quite so inadequate, I can move on. Here's how Dr. Cox describes Langer's lines.
The actual configuration of the incised wound is dependent on whether the edge of the sharp instrument was parallel, transverse or oblique to the direction of the alignment of the collagen fibers in the skin; this alignment is referred to as Langer's Lines. Langer's lines, also called cleavage lines, is a term used to define the direction within the human skin along which the skin has the least flexibility. These lines correspond to the alignment of collagen fibers within the dermis. ... Knowing the direction of the Langer's lines within a specific area of the skin is important for surgical operations, especially cosmetic surgery. Usually, a surgical cut is carried out in the direction of Langer's lines, and incisions made parallel to Langer's lines generally heal better and produce less scaring. ... 
If an incised wound occurs parallel to Langer's lines it will tend to be narrow in configuration with the wound edges being more closely approximated than one in [sic] which runs across or oblique to Langer's lines. In the latter instance, you can expect the wound edges to be further apart with the configuration of the incised wound being more oval than linear with the wound edges being pulled apart and everted [turned inside out]. The orientation of stab wounds relative to Langer's lines can have a considerable affect [sic] upon the presentation of the wound.
If you look again at the wounds and compare them to the Langer lines for that region, you can see that Shandra's neck wound is nearly parallel to her Langer lines. Her neck wound is more slender, less gaped, than her chest wound and Marcell's chest wound.

The two chest wounds are almost perpendicular to the local Langer lines. They are gaped open far more than Shandra's neck wound.

According to Dr. Cox, we cannot determined from the chest wounds whether or not the weapon had a single or double-edge blade. The neck wound, however, is compelling evidence that the weapon had a double-edge blade. Unless a different weapon was used for the chest and neck wounds, the knife found in the bottom of a box in Preston Hughes' closet is not the weapon that killed LaShandra Rena Charles and Marcell Lee Taylor.

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Anonymous said...

While I am truly flattered that my pseudonym has stuck in your head, I must concede that it was not me that gave the answer to Brain Teaser #2 to which you are referring. That was actually reader Paul. I was the first person to be awarded Skeptical Juror point with my answer to Brain Teaser #1.

- Lando

tsj said...

Oops! I've corrected my grievous error.

Lindsey said...

Fascinating! This is so informative and interesting. Thank you for sharing this information. I was wondering why the stab wounds were drastically different from the neck vs the chest wounds, and the Langer's Lines explain it all.

tsj said...

Thank you. I've become pretty much impervious to negative criticism, but I admit to still being susceptible to positive feedback such as your comment. Thank you especially for the exclamation mark!

Anonymous said...

Good stuff, TSJ!

Anonymous said...

This is your best and I think only argument that could get Preston off. However the two things that could derail it, are that it was discussed at the trial and the jury heard that there was a possibility that it might not have been the knife or that the ME explained why the cuts didn't have a blunt edge. But I also think the argument would have to come from a ME that looks at it and agrees with you.


tsj said...

I have more up my sleeve. Much more.

Anonymous said...

I'll be waiting. But as we both know this case has moved beyond the trial stage so now the burden of proof is much higher to get a pardon or a reduced sentence. And his other problem is that since he's had several other appeals the court doesn't like an appeal just for an appeal purpose. As they said in the last appeal he needs to prove his innocence, not just show doubt. They either need to find the person who did it, or pull up some new evidence.


Unknown said...

Sorry to be so late to the party, but I also wanted to state that I found this analysis to be a very compelling argument in favor of innocence.

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