Sen. Ted CruzRafael (Ted) Edward CruzOvernight Health Care: Democrats attack after Trump revives talk of ObamaCare replacement | Cruz, Ocasio-Cortez efforts on birth control face major obstacles | CVS investing M to fight teen e-cig use Overnight Health Care: Democrats attack after Trump revives talk of ObamaCare replacement | Cruz, Ocasio-Cortez efforts on birth control face major obstacles | CVS investing M to fight teen e-cig use Biden says he will beat Trump in Texas, Georgia and South Carolina 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 SasseSwing-state Democrats see trouble in proposed pay hike Swing-state Democrats see trouble in proposed pay hike House Dems move to give lawmakers a pay increase 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'RourkeProgressive activist: Democratic nominee will 'need to ride a little bit to the center' Poll: Biden leads Sanders by 22 points Poll: Biden leads Sanders by 22 points MORE (D-Texas). The nonpartisan Cook Political Report rates the race a "toss-up."