Bullet Lead Analysis Revisited

The most well-known rifle shots in history are those fired November 22, 1963 from a Mannlicher-Carcano rifle in Dallas' Dealey Plaza. These were presumably fired by Lee Harvey Oswald. The bullets that killed President John F. Kennedy have ever since been the subject of controversy between the government investigators and a plethora of conspiracy theorists. The official version of the assassination is that a single crazed gunman fired the fatal shots from a sixth floor window in the Texas School Book Depository building. Various attempts to demonstrate multiple shooters on the infamous "grassy knoll" and other locations have tried to show that the assassination of the President was a conspiracy of two or more shooters.

Audio analyses performed on recordings from that event appear to show that four or more shots were fired, implying the presence of more than one gunman. However, the acoustical layout of Dealey Plaza is such that the scientific validity of those studies was called into question. Various films, pictures and eyewitness testimony implicate an additional shooter at the grassy knoll area. Then there is the infamous "magic bullet" which presumably passed thru Kennedy, then struck Texas Governor John Connally in the back, breaking four inches of one of his ribs, passing out and into his arm, and eventually lodging in his right wrist; one of the hardest bones in the body. Then this bullet, in almost pristine condition, fell out onto the stretcher as he was brought into Parkland Hospital. In all that travel, the bullet that had lost no more than 1.5 percent (2.5 grains) of its mass.

Bullet Lead Analysis of Bullet Fragments

In all, five bullet fragments were recovered from Jack Kennedy's body at autopsy and from the Presidential limousine. The original chemical analysis on these lead fragments was performed by the FBI Laboratory and by a University of California, Irvine, chemist, the late Vincent Guinn. Using the presumed best methods of the day, Guinn conducted trace metal analysis on the fragments and concluded that Kennedy was killed by two bullets, both fired from Oswald's rife.

Forensic chemical analysis in the 1960s was not as sensitive and sophisticated as it is today. Chemical and metallurgical analysis methods and instrumentation have made major advances in accuracy and sensitivity in the past forty years. The analyses performed by forensic metallurgy labs today can detect much lower levels of trace metal elements with much higher levels of accuracy and confidence.

In 1976, the FBI reported that from their analysis of the composition of the fragments, it was not possible to tell definitively if the fragments came from the same bullet. However, Guinn's conclusion was very different. He concluded that the levels of the trace element antimony came from two bullets fired from a Mannlicher-Carcano rifle. Therefore, there was only one shooter, Oswald. These results were the basis for the Warren Commission's conclusion that there was only a lone gunman.

Bullet Lead Composition

When lead is smelted and refined, the process is designed to remove contaminant elements like silver, antimony, and copper and reduce their level to that acceptable for a specific alloy or composition. Studies have shown that the level of micro-contaminant metals in bullets is not unique. Bullets poured from different batches of lead smelted months or years apart could have an identical chemical signature. In addition, bullets poured from the start of a batch could differ measurably from those poured at the end of the batch. Therefore, trace metal analysis of bullet lead does not provide a reliable chemical fingerprint like trace chemical analysis does in other areas.

In 2004 and 2006, researchers at Lawrence Livermore Laboratories in California showed that there was much more variability in Guinn's analysis in the levels of trace metals, like silver and antimony. The major problem with the analysis resides in the data analysis and interpretation of the results. In 2002 the FBI enlisted the help of the National Academy of Sciences' National Research Council (NRC) to conduct an independent study of the bullet lead analysis method, using independent experts in the field. The NRC's final report expressed significant concerns over the interpretation of bullet lead examination. The FBI still stands by its procedures as being valid for evidence purposes. However, this and other data has led the FBI laboratory to announce officially in September 2005 the discontinuation of bullet lead examinations. Since then, this evidence has been suppressed by courts in several states and will undoubtedly be challenged in a great number of future cases.

Kennedy Assassination Fragments Revisited

Because of the historic significance of the bullets fired in Dallas that day, bullets from the same brand and lot as used in the assassination have been preserved as collector's items and are still available today. A group of researchers at Texas A&M University have undertaken a project to reanalyze these bullets by more modern procedures, because they believe it is desirable to reevaluate the evidentiary value of this data. The group includes researchers William James and Cliff Spiegelman, and the FBI Laboratory's former chief metallurgist, William Tobin. Tobin, before his retirement, has been involved in a multitude of analysis projects including the bombing of the Murrah Federal Building in Oklahoma City and the crash off Long Island of TWA Flight 800. He has for many years questioned the FBI's methods used to match bullets to crime suspects.

After the NRC's report, the National Academy of Sciences developed new guidelines for accurate and proper bullet analysis. Following these guidelines, Tobin and his co-workers reanalyzed the evidence presented to the House Select Committee on Assassinations in 1976. This was the evidence that determined that a lone shooter (Oswald) was Kennedy's killer.

Conclusions Revisited

Five bullet fragments were used in the analysis by the FBI lab and Guinn. These were retrieved from Kennedy's body (2), Connally's wrist (1), the bullet on the stretcher at the hospital and from the Presidential limousine (2). In an article recently published in the Annals of Applied Statistics, these authors conclude that "the evidence [antimony levels] used to rule out a second assassin is fundamentally flawed". Based on careful statistical analysis of the trace metal data, they believe that Guinn used an analytical method and certain statistical assumptions that were faulty. They further assert that their findings "mean that the bullet fragments from the assassination that match could have come from three or as many as five separate bullets".

Tobin and his colleagues do not definitely conclude that more than one shooter was present that day in Dallas. However, they do say "that if the fragments came from three or more separate bullets, then a second assassin is likely, as the additional bullets would not be attributable to the main suspect, Mr. Oswald".

Forensic analysis is a dynamic science and new instrumentation and methods are always being developed to provide more and better quality evidence. Sometimes, as in this case, data from older methods may have to be reevaluated. It is important for law enforcement officers and prosecutors to remember that forensic evidence is only a part of the puzzle. It should not be the only evidence on which a case is based. Forensics cannot replace basic investigation procedure and evidence gathering; it can only supplement it.