Reply #12: the truth is, they HAVE talked

[Minstrel Boy]

But it disappears into the official memory hole. And some people just don't want to know about it, whatever the evidence and how many the confessions. There's a book devoted to this very subject, with respect to the JFK assassination, titled Someone Would Have Talked, which records the words of those who knew, and who DID speak.
http://jfklancer.com/catalog/hancock/index.html

Some who spoke:

Jack Ruby (statement to reporters after his trial: "Everything pertaining to what's happening has never come to the surface. The world will never know the true facts, of what occurred, my motives. The people that had so much to gain and had such an ulterior motive for putting me in the position I'm in, will never let the true facts come above board to the world." Reporter: Are these people in very high positions Jack? Ruby: "Yes.")
Santos Trafficante (Told attorney Frank Ragano in 1987: "Carlos (Marcello) fucked up. We shouldn't have gotten rid of Giovanni. We should have killed Bobby.")
David Ferrie (overheard by Richard Giesbrecht in the Winnipeg airport on Feb 13, 1964, telling a companion he was concerned about how much Oswald had told his wife about the plot, wondering why they'd ever used him, and mentioning they had more money than ever. Giesbrecht said the man "had the oddest hair and eyebrows I'd ever seen" and immediately contacted the FBI. He positively identified Ferrie. After questioning Giesbrecht and telling him that his information was important and "the break we've been waiting for," the FBI contacted him several months later and told him to forget about the matter since it was too serious and since he was a Canadian, there would be nothing the FBI could do for him if he needed protection.)
Johnny Roselli
David Atlee Phillips (head of hemispheric operations for the CIA, stationed in Mexico City. Seen in Oswald's company the summer of 1963 by Alpha 66 leader Antonio Veciana. When dying of cancer, Phillips tearfully confessed his guilt to his brother)
Frank Sturgis (CIA operative. Told The San Francisco Chronicle of May 7, 1977 that "the reason we burglarized the Watergate was because Nixon was interested in stopping news leaking relating to the photos of our role in the assassination of President Kennedy.")

"Nobody talked" is a lie told by those who don't want to hear what they say.