Nikita, the “got” implies “extremely high probability.” Paraphrased, “I don’t know for sure that somebody will talk, but knowing human nature it is practically certain that somebody in the joint will talk.” Without the “got,” it would sound like the speaker somehow knows that a particular person in the the joint would talk. Another example, suppose a crime happens in a crowded place. “Somebody’s got to have seen what happened” means “Because it was so crowded, the chances are really high that somebody saw what happened.” In contrast, “Somebody saw what happened” would be a factual statement that a person did see.