Final answer:
Agent Alvin Dewey provided the first details of the Clutter family murder case to the press, revealing the victims and the lack of forced entry.
Step-by-step explanation:
Agent Alvin Dewey was a key figure in the investigation of the Clutter family murder case in the book 'In Cold Blood' by Truman Capote. After the arrest of the suspects, Agent Dewey held a press conference and provided the first details of the case to the press. He revealed that four members of the Clutter family, Herbert, Bonnie, Nancy, and Kenyon, had been brutally murdered in their home in Holcomb, Kansas. He also mentioned that there were no signs of forced entry and that the motive for the crime was still under investigation.