Complex sentence: Another milestone came with the 1966 study by Henry K. Beecher, published in the New England Journal of Medicine, which became instrumental in the implementation of federal rules on human experimentation and informed consent.
Split into simpler sentences: Another milestone came with Henry K. Beecher's 1966 study as published in the New England Journal of Medicine. His study became instrumental in the implementation of federal rules on human experimentation and informed consent.