Jim (Phiilips’s brother) knew that David was the head of the "Retired Intelligence Officers of the CIA", or some such organization, and that he was extremely critical of JFK, and his policies. Jim knew at that point, that David was in some way, seriously involved in this matter and he and David argued rather vehemently, resulting in a silent hiatus between them that lasted almost six years according to Jim. Finally, as David was dying of irreversible lung cancer, he called Jim and there was apparently no reconciliation between them, as Jim asked David pointedly,
"Were you in Dallas on that day"? David said,
"Yes", and Jim hung the phone up.