THE CASE OF THE POSSIBLE SECOND SHOOTER
The Evidence: In 1976 the House Select Committee on Assassinations ordered a reinvestigation of the murder of Martin Luther King Jr. Specks of metal visible in King's scalp in autopsy photos (left, top) suggested to some that brass from a railing in front of him had ended up on his body. Given the angle from which James Earl Ray shot, he could not have hit the railing. Was there a second gunman?
The Science: Examining a surviving microscope slide under a polarizing microscope, Palenik noted that the metal specks bore marks from the slicing instrument used to prepare them for mounting. That implied they were soft-most probably lead, not brass. Palenik cut through the slide cover, removed a sample, and halved it. First, the low-tech approach: He dissolved half the particle in solution, let it dry, then added potassium iodide. The ensuing reaction produced the yellow hexagonal plates typical of lead iodide (left, bottom). Next Palenik microprobed the other half with an X-ray spectroscopy detector, which provides elemental analyses. The result: lead again. The metal in King's scalp came from a bullet, not the railing, Palenik concluded. There was no second gunman.