There are a number of potential sources for error in plotting a trajectory using the method described above. The creation of the objects, positioning of those objects, and locating the wounds are all possible sources of statistical error. Despite the rigorous checks that were performed to minimize these errors, it is important to understand that statistical errors are inevitable. It is equally important to note that these errors are minimal and within margins anticipated with this type of recreation.
For instance, blueprints from the 1978 restoration project were used to construction the model of the Texas School Book Depository. Upon completion, the dimensions of the sixth floor sniper's nest window were checked against the actual window dimensions provided by officials from The Sixth Floor Museum at Dealey Plaza. The model was found to be within one inch of the actual dimensions. This shows the overall model to have a better than 99.9% accuracy level - well within tolerances for this project.
Because the construction of Dealey Plaza was based on survey maps, a high degree of accuracy was obtained, particularly in the creation of Elm Street - a crucial feature in establishing any assassination trajectory. The slope of the road, and its relationship to the Book Depository were among the many details available in the 1978 Drommer & Associates survey map. The Elm Street portion of the Dealey Plaza model shows a better than 99.4% accuracy level.
The positioning of the limousine is another potential source of error, although much less so than other sources. By matching the speed of the limousine model to the actual limousine seen in the Zapruder film, these potential errors are further reduced. The film's multiple frame count provides a "sample rate" that assures a close alignment. At any given frame, the limousine model is calculated to be within 4 inches of its real world counterpart. The error associated with this figure would be negligible on any trajectory analysis.
The greatest source of potential error lies in positioning the occupants in the limousine since their positions will determine the relationship of the entrance and exits wounds to the environment of Dealey Plaza, and hence, any plotted trajectory. Potential errors in establishing the correct relationship between the wounds and the environment can be depicted through the use of trajectory cones.
|To illustrate the potential error associated with positioning JFK and JBC at the time they were apparently both struck by a single bullet (Z223), two cones were created. The apex of both cones converge at a single point that lies along the calculated straight-line trajectory path between the exit wound in JFK's throat and the entrance wound in JBC's back. Both cones are then splayed in opposite directions; one forward along the path toward JBC's back wound (illustrating potential errors in positioning of JBC's back wound in 3D-space) and the other backward toward JFK's throat wound (illustrating potential errors in positioning JFK's throat wound in 3D-space).|
The point at which the apex of the two cones converge lies closer to JFK's throat wound because the potential error associated with the placement of that exit wound in 3D space is less than the error associated with fixing the position of the entrance wound in JBC's back.|
It was determined that except for turning his head approximately 54 degrees to the right (accompanied by a very slight torso rotation), then back to a nearly forward position, there were no major changes in JFK's posture after about Zapruder frame 161 (a conclusion also reached by the HSCA Photographic Panel [6HSCA44]) Forensic pathologist Dr. Clyde Snow told the HSCA that laboratory tests showed that the elasticity of the skin would have caused the position of the exit wound in JFK's throat to move only slightly from the position shown in the autopsy photographs - approximately 0.04 inches to the right and 0.4 inches upward. (6HSCA45) This of course, is nominal.
The greater potential error lies in fixing the 3D position of the entrance wound in JBC's back. As explained earlier (see positioning errors), there could be up to a 6 degree rotational error (heading, pitch, bank) in matching JBC's position to any point in the Zapruder film (particularly in the earliest portions of the film, less in later portions). A 6-degree rotational error would move the entrance wound on JBC's back up to an inch in any direction.
|To illustrate these potential errors, two 6-degree cones were created and positioned as described above at the equivalent of Zapruder frame 223 - the last frame before impact. All possible firing sources for the bullet that passed between the exit wound in JFK's throat and the entrance wound in JBC's back now fall within the dimensions of the cone. Although the trajectory cone edges are shown as "hard," it is important to understand that as potential trajectories in the 6 degree error range move away from center, the probability diminishes. This is largely due to the fact that the potential errors in JFK and JBC's rotational position also diminish in that range.|
|The cumulative total errors associated with the construction and placement of other objects in the scene is negligible when compared to the potential errors in placing the wounds and the position of those wounds in 3D-space. Therefore, the trajectory cones used in this analysis are considered sufficient to describe potential errors in the computer recreation.|
Projecting the error cone rearwards 200 feet finds that it intersects the southern-face of the Texas School Book Depository, at the level of the fifth and sixth floors, as well as a small portion of the northwestern-most roofline of the Dal-Tex Building. The error cone's intersection of the southern-face of the Depository can be described as an ellipse (due to the angle of the cone in relation to the building) that is approximately 26 feet in diameter. The source of the shot that struck JFK in the upper-right back, emerged from his throat, and went on to strike JBC in the right-back must lie somewhere within the confines of this area.
The portions of both the Texas School Book Depository and Dal-Tex Building which fall within the limits of the cone are shown at left. Four windows of the Depository lie within the area defined by the cone. Photographs show two of the four were open at the time of the shooting. The open window on the fifth floor was occupied by eyewitnesses. The sniper's nest window - the southeast corner, sixth floor (arrow) - is the only open, unaccounted for window that lies within the area defined by the trajectory cone.|
This is the location where eyewitnesses saw a rifle being fired from, and where Dallas police later found three spent rifle shells.
A portion of the northwest roofline of the Dal-Tex Building also lies within the trajectory cone. Unlike the Texas School Book Depository sniper's nest window, there are no eyewitness accounts of a gunman firing from the Dal-Tex Building roof, nor was any physical evidence ever found to suggest that shots had been fired from that location. It is also worth noting that a gunman positioned within the defined roof area would not have been able to fire the fatal shot at Zapruder frame 313. A perspective view from the northwest corner roofline of the Dal-Tex Building shows the presidential limousine blocked by the southeast corner of the Book Depository at the time of the fatal head shot. It seems unlikely that anyone intent on killing the president would have positioned themselves at the northwest corner, when a position further south along the roofline would have afforded them a clear view of the entire length of Elm Street.|
In conclusion, a trajectory track projected rearward from JBC's chest wound at Zapruder frame 223 intersects the southeast corner window of the sixth floor of the Texas School Book Depository. A trajectory cone, used to illustrate the potential errors of the computer recreation, also points to the sniper's nest as the source of this shot. Although the northwest roofline of the Dal-Tex Building is included in the trajectory error cone, other facts (in particular, the firearms evidence which proves that the bullets that struck Kennedy and Connally were fired from the Mannlicher-Carcano rifle found on the sixth floor of the Depository to the exclusion of all other weapons) exempt it as a source of the gunfire.|
It is further concluded that the relative positions of JFK and JBC at Zapruder frame 223 supports the theory that one bullet struck both men. Both the trajectory track and the trajectory error cone provide a high degree of probability that a single bullet passed through JFK's upper torso before striking JBC in the back and exiting his right chest.
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