Complex sentence: Wilma and Betty see this on the news, and break into Slate and Co. to get the dictabird, the only witness who can clear Fred, unaware that Cliff saw them from his office window.
Split into simpler sentences: Wilma and Betty see this on the news, and break into Slate and Co. to get the dictabird, the only witness who can clear Fred. They are, however, unaware that Cliff saw them from his office window.