Sen. Ted Cruz on Wednesday tweeted an image with the symbol used by the Zodiac Killer, a joke referring to a conspiracy theory floated during the 2016 GOP primary that the Texas Republican was behind the unsolved murder spree in northern California in the 1960s and 1970s.

Cruz posted a picture of one of the encrypted letters the Zodiac Killer sent to Bay Area media organizations as part of a light-hearted Twitter exchange with Nebraska Republican colleague Sen. Ben Sasse.

Sasse had apologized to Cruz for spilling soda on him during U.S. Attorney General Jeff Sessions' testimony before the Senate Judiciary Committee, which the pair attended.

"Full disclosure: I was wearing my 'Lee Harvey Oswald Was Framed' t-shirt," Sasse tweeted in response to a Twitter user who said he would have done worse than pour Dr. Pepper on Cruz if he had been "sitting with the son of the guy who killed Kennedy."

The duo's reference to President Trump's claim in the lead-up to the 2016 GOP primary that Cruz's father helped John F. Kennedy's assassin, citing how the elder Cruz was photographed with Oswald in 1963, triggered Cruz's reaction on social media.

Cruz has vehemently denied the Oswald accusation.

The identity of the Zodiac Killer, who was confirmed to have slain at least five people, was never uncovered.