Randich and by former FBI Chief Metallurgist, William Tobin. The 2002 Tobin/Randich paper prompted the National Academy of Sciences (Board on Chemical Science and Technology) to review the science of bullet lead analysis. In a report in 2004 the NAS found the scientific basis for matching bullet sources from the analysis of bullet lead composition as practiced by the FBI was flawed. As a result of that report, the courts appear to have stopped accepting this evidence and the FBI has stopped using bullet lead analysis for forensic purposes. The NAS report on CBLA, and its relevance to the Guinn's analysis of bullet lead in the JFK assassination, is the subject of comment by Randich and Grant in their 2006 paper at page 719. Criticisms of the single-bullet theory Critics of the single-bullet theory state that it is not possible that a single bullet could cause the number of wounds it did and still remain nearly intact. Some critics state that discrediting the theory would suggest the involvement of two shooters. Analysis based on Zapruder film and physical evidence Critics of the single-bullet thesis question not only the bullet's trajectory and relative lack of damage, but also the question of timing of hits to both the president and Connally. A single bullet would have passed through both men in less than 1/100th of a second, which means that a strike of both men by a single bullet would have happened too quickly to be caught on more than a single Zapruder frame (these were exposed at 1/18th second intervals). From the Zapruder film one can see Kennedy with his hands in front of his chest near his throat as he emerges from behind the sign at Zapruder frame 225. According to one popular version of the single-bullet theory (promoted by Gerald Posner in his book, Case Closed), the interval between frame 223 and 224 is the time the same projectile passes through both Kennedy and Connally's body. It is not obvious at this point (frame 224) whether Connally has, or has not, been hit; however, Connally, but not other limousine occupants, is newly blurred in frame 224 but not in frame 223. Connally himself, in analyzing the frame-by-frame Zapruder film, identified his own hit later, at about Zapruder frame 230, whereas Kennedy is certainly hit about Zapruder frame 224, a third of a second earlier. Beginning immediately after frame 224,