In the premiere of a chronicle of the hunt for California's Zodiac Killer, who murdered at least five people in the San Francisco Bay Area in the late 1960s and early '70s, a prime suspect with code training emerges.

The hunt uncovers clues that the Zodiac Killer may have served in the U.S. Armed Forces, as the team's supercomputer identifies strange symbols in the killer's code that would have been known to only a few when it was written.

A mysterious new cipher related to the Zodiac Killer is discovered, while the team's supercomputer uncovers a strange lunar pattern linking the murders. Also: A taunting riddle by the killer may lead to a body; and a second prime suspect emerges.

The hunt goes into high gear as the FBI releases secret files; and a handwriting analyst connects the Zodiac Killer's letters to a taunting correspondence mailed 3000 miles away in Albany, N.Y.

Sal and Ken investigate the epicenter of the murders. A team member solves the Zodiac's infamous Z340 code, which has eluded codebreakers for 50 years.