Why do the reporters think haldeman is the 5th man how do they get the verification?

Reporters believe Haldeman is the "fifth man" based on a combination of insider information and investigative leads suggesting his involvement in the Watergate cover-up. They connect him to other key figures and events tied to the scandal, such as his role in the Nixon administration and communications intercepted during the investigation. Verification comes from corroborating testimonies, documents, and the patterns of actions taken by those in the Nixon administration, which align with the evidence pointing to Haldeman's complicity.