The blood-stained knife found in Arthur Leigh Allen's home that never sealed the Zodiac case

The knife came out of Arthur Leigh Allen’s home in 1991, and it was bloody.

A Vallejo task force found it during a search of the suspect’s house, part of the long investigation into the Zodiac murders that spanned California from December 1968 to October 1969.

They also found a hooded costume.

The discovery fueled suspicion; it looked like something out of the case file.

But no conclusive evidence ever linked the knife to the crimes.

The source does not establish that the knife was used in any Zodiac attack.

It does not specify whose blood was on it.

It does not even say exactly where in the home the knife was found, or describe its condition beyond that single word: bloody.

A survivor had picked Allen from a photo lineup, and the task force, including a Vallejo detective, had focused on him.

The knife seemed to fit a pattern.

It was evidence of something.

It was not evidence of the Zodiac.

Allen was never charged with any of the murders.

He died in 1992, a year after the search.

The knife sits in the record as a question mark—a blood-stained object that pointed at a man but proved nothing about him.

THE ATTACKS AND THE LETTERS

Between December 1968 and October 1969, a serial killer known as the Zodiac murdered at least five people in the San Francisco Bay Area.

The confirmed attacks were shootings at a remote road in Benicia, then at Blue Rock Springs Park in Vallejo.

Then a stabbing at Lake Berryessa.

Then the shooting of a taxi driver in San Francisco's Presidio Heights.

The killer sent taunting, cryptogram-laden letters to newspapers.

He coined the name "Zodiac" himself, in his own hand.

Police linked the attacks through ballistics, survivor testimony, and the killer's own letters.

Ballistics matched some of the shootings. Survivors described the same man. The letters claimed the rest.

One cipher, cracked by a Salinas schoolteacher and his wife, contained a boastful confession.

It read as a claim of authorship over the murders.

The killer's identity is not established in the record.

No one was ever arrested or tried for the murders.

No trial occurred, so there were no prosecutors, no defence attorneys, no judge.

The letters were the closest thing to a witness statement.

They were taunting. They were cryptogram-laden. They were audacious.

Each envelope widened the fear.

The taxi driver's killing came eleven days after the Lake Berryessa stabbing.

The killer wrote again.

The record holds his words, his ciphers, his claimed body count.

It does not hold his name.

THE SUSPECT AND THE SEARCH

The task force in Vallejo turned to Arthur Leigh Allen in 1991.

A surviving victim had picked him from a photo lineup.

Detective Jack Mulanax was part of that task force.