Final answer:
Klaus Fuchs knew the atomic bomb information and passed it to the Soviets, leading to the arrest of several individuals, including the Rosenbergs.
Step-by-step explanation:
The person who had actually known the information that was on the second test was Klaus Fuchs, a British physicist. Fuchs admitted to passing information about America's atomic bomb secrets to the Soviets, thereby accelerating their development of an atomic bomb. His confession led to a series of investigations and arrests, which further implicated Harry Gold, David Greenglass, and finally Ethel and Julius Rosenberg, infamously known for being executed for espionage related to this breach of atomic secrets. The distribution of these secrets is believed to have allowed the Soviets to construct their atomic bomb roughly 18 months earlier than anticipated. This network of espionage deeply concerned the American public and authorities during the post-World War II era, especially in light of the Cold War tensions.