Due to the graphic nature of today's crimes, listener discretion is advised.

Extreme caution is advised for listeners under 13.

Today is Monday, April 20th, 2020.

On this day in 1970, the notorious Zodiac Killer

sent one of his most disturbing communications to the San Francisco press.

The letter not only held the key to the killer's identity,

but it also included a detailed bomb threat that terrified the public.

Welcome to today in true crime, a parcast original. Today we're covering the My Name

is, Cypher, one of several cryptic messages the Zodiac Killer sent to Bay Area newspapers.

Let's go back to San Francisco on April 20th, 1970. As the Sun rose over the city, the Zodiac Killer slipped an envelope with the

cipher into an unknown postbox and fled the scene as quickly as possible.

The next morning, the letter was rushed to the editor of the San Francisco Chronicle. He wasn't surprised to see another message from the

Zodiac. Over the past year, the paper had grown accustomed to hearing from the mysterious

serial killer every few months. But the Zodiac still knew how to keep

reporters on their toes. By the time the editor had finished reading the

killer's latest message, he was aghast.

For the second time, the Zodiac had threatened to blow up a school bus full of children.

In a previous letter, the Zodiac had included a hand-drawn diagram of an explosive

device he planned to build. The plans showed it would be placed on the side of the road and rigged to blow up as a school bus drove by.

After examining it, the FBI had determined that the plans for the device were theoretically sound.

It was no idle, doodle, or empty threat.

It was possible the Zodiac had an actual plan that could result in a devastating explosion.

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