Sen. Ted CruzRafael (Ted) Edward CruzMichael Bennet declared cancer-free, paving way for possible 2020 run Booker, Harris have missed most Senate votes O'Rourke sweeps through Virginia looking to energize campaign 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 SasseSenate needs to stand up to Trump's Nixonian view of the Fed GOP senators divided on Trump trade pushback The Hill's 12:30 Report: Assange faces US charges after dramatic arrest 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'RourkeRobert (Beto) Francis O'RourkeSanders announces first endorsements in South Carolina On The Money: Cain 'very committed' to Fed bid despite opposition | Pelosi warns no US-UK trade deal if Brexit harms Irish peace | Ivanka Trump says she turned down World Bank job Ex-Obama campaign manager: Sanders can't beat Trump MORE (D-Texas). The nonpartisan Cook Political Report rates the race a "toss-up."