The Zodiac Killer

CHICAGO -- Even on his days off from working overnights for the Chicago police, John Lewison usually stayed up through the night and slept during the day.

It was often early in the morning, after having his fill of CNN, that he turned to a hobby of sorts. Sprawled on a couch in a T-shirt and sweatpants, Lewison tried to unravel a murder mystery that has mystified law enforcement and crime buffs for decades: the identity of the Zodiac killer, who is believed responsible for at least five homicides in the San Francisco Bay Area in the late 1960s.

Lewison, who has risen to lieutenant in nearly 25 years with the department, thinks he's come up with a solution to one of a series of coded messages the serial killer sent along with taunting letters to the news media.

The cryptograms, composed of alphabetic, mathematical and astrological symbols, are thought likely to contain vital information about the suspect. Many of the letters included what became the Zodiac's signature line: "This is the Zodiac speaking." The slayings not only piqued the curiosity of police detectives in Northern California but also amateur investigators, scholars and true-crime buffs throughout the country.

Lewison worked on and off for a few years on solving one particular 32-character cryptogram. In the puzzle, from 1970, Zodiac had threatened to have planted a bomb and sent a road map to ostensibly help in the search.