we really don't know the full dimensions of the case, but we know he's the zodiac because he started writing to the police, claiming credit in great detail, articulating and explaining what he did to these victims. >> "the chronicle" received two letters. they notified us immediately. the criminologist was sent over to the newspaper, as were inspectors, and the two letters were examined and opened. >> the zodiac's reaching out to the police repeatedly and in great length was something new. >> the psychotic killer has already murdered five, one at a lovers' lane near a lake just north of san francisco, three others in nearby vallejo, the latest a taxi driver in san francisco. the zodiac killer seems to crave publicity. he sent letters and cryptograms to newspapers and the police, recounting his crimes, threatening more murders, and making bay area residents very edgy. >> in the '70s, there was a