A brief résumé. Josiah “Tink” Thompson, the subject of this Op-Doc, graduated from Yale in 1957, became a demolitions expert and frogman for the Navy, and then returned to Yale to get his Ph.D. on the Danish philosopher Soren Kierkegaard.

The Kennedy assassination changed Tink’s life. In 1967, he was an assistant professor of philosophy at Haverford, when he published “Six Seconds in Dallas.” Short, simple and quietly convincing, it is still one of the best books written about the assassination.

Ten years later, Tink left academia and became a private detective in Northern California. Now he has returned to what has haunted him for 50 years: Frame #313 of the Zapruder film, and our inability to come up with a definitive account of what happened in Dallas.

Is there a lesson to be learned? Yes, to never give up trying to uncover the truth. Despite all the difficulties, what happened in Dallas happened in one way rather than another. It may have been hopelessly obscured, but it was not obliterated. Tink still believes in answers, and in this instance, an answer. He is completing a sequel to “Six Seconds” called “Last Second in Dallas.” Like its predecessor, this book is clearly reasoned and convincing. Of course, there will be people who will be unmoved by his or any other account. This is a dogfight with too many dogs in the fight. Most people have already staked out their commitment.