The two reporters who had a secret informant that break the watergate scandal wide open were:
carl bernstein
archibald cox
alexander butterfield
bob woodward

The answer is 1) Carl Bernstein and 4) Bob Woodward

Both Carl Bernstein and Bob Woodward were two Americans investigative journalists of The Washington Post when they were assigned the task to cover a break-in at the Watergate office complex in June 1972. They became very famous for recollecting and revealing information (By anonymous sources and by an interview with bookkeeper for Nixon) about the government's corruption, mishandling of funds and destruction of records, in which President Richard Nixon was involved.

Their discoveries led to further police investigations of the President, in which he, indeed was found guilty. In 1974, Nixon determined to resign in order to avoid facing impeachment.