Sen. Ted CruzRafael (Ted) Edward CruzThe Hill's Morning Report - Trump grapples with Turkey controversy This week: Congress returns to chaotic Washington The Hill's Morning Report - Lawmakers return to work as Dem candidates set to debate MORE (R-Texas) tweeted a letter from the Zodiac Killer in an apparent Halloween joke Wednesday.

The once-popular meme that Cruz is the Zodiac Killer emerged during the 2016 Republican presidential primary. The letter shows the Zodiac's cryptography, which he sent to newspapers during his killing spree.

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Five people in Northern California were killed by the Zodiac, who was never identified, in the late 1960s and early 1970s.

Cruz's wife, Heidi, denied her husband being the Zodiac killer, calling it “a lot of garbage." Cruz was born two years after the first killings.

Cruz had previously tweeted this image last year joking with Sen. Ben SasseBenjamin (Ben) Eric SasseHong Kong protesters trample, burn LeBron James jerseys in wake of comments This week: Congress returns to chaotic Washington Trump's GOP impeachment firewall holds strong MORE (R-Neb.) about a soda that he spilled on Cruz.

The Republican senator is locked in a tight reelection campaign with Rep. Beto O'RourkeBeto O'RourkeWarren defends, Buttigieg attacks in debate that shrank the field Warren leads in speaking time during debate Democrats wrangle over whether to break up Big Tech in debate first MORE (D-Texas). The nonpartisan Cook Political Report rates the race a "toss-up."