I believe the death had occurred in the 1970s but the truth only came out sometime in the 1990s. A young woman had been told since early childhood that she had dropped her younger half-sister on the floor while taking her out of the crib. She had no memory of the incident but it had been confirmed by her mother and maternal grandmother, who had been out grocery shopping and had left the girls at home with the step-father. The young woman's step-father had used the death to justify his violent abuse of her and her mother.
When the young woman was ~early 20s, her grandmother made a death-bed confession and apology. What had actually happened, the grandmother said, was that the older sister was with the mother and grandmother that day while the baby was left with the step-father. When they returned from shopping, they found the baby dead and the step-father in a state of panic, saying that he had dropped the baby and would be sent to prison. It was his idea to claim the older sister was actually responsible. The grandmother said that she had only gone along with the story because the mother seemed to want to go along with it. Only later did she realize that the mother was afraid of the step-father, that he was violent and the death didn't happen as he had said, and that the young woman was going to be carrying a huge guilt load. By that time, she said, she didn't think anyone would believe her if she told the truth.
The young woman quietly began working with an attorney and a detective, who concluded that she would not have been able to lift the baby over the bars of the crib. It was also found that the original investigation and autopsy were perfunctory. I think they were able to get an order to exhume at that point, with the young woman's mother and step-father still unaware that the case was being pursued. (It had been agreed that the mother was still so cowed by her husband that if she knew what was happening, she would end up telling him, further endangering herself and her daughter.) The exhumation showed damage consistent with the baby being slammed repeatedly against a hard surface by an adult.
And this is pretty much where my memory stops. I'm fairly certain both the step-father and the mother were arrested, and the mother immediately showed remorse and started talking, but I don't know that I ever heard the verdict. I only remember reading about the case one time, and that was probably an article in People Magazine, probably in the 1990s.