On a historic day in US politics, one Congressman used the main event to amplify a conspiracy theory that has rapidly been moving into the mainstream.

Representative Paul Gosar tweeted this during the first day of public hearings in US President Donald Trump's impeachment proceedings:

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Fairly standard stuff from a man with both feet firmly in the Republican camp.

In his next 22 tweets over several hours, Mr Gosar continued to comment on the hearings.

By the time he had finished, people had noticed a pattern.

The first letters of his tweets, in order, read: E-P-S-T-E-I-N-D-I-D-N-T-K-I-L-L-H-I-M-S-E-L-F.

"Epstein didn't kill himself" refers to the death in August of convicted sexual predator Jeffrey Epstein, who was found by a New York City medical examiner to have taken his own life in his jail cell as he awaited a new sex trafficking trial.

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With his links to rich and powerful people, including Mr Trump himself, former US president Bill Clinton and Britain's Prince Andrew, it was inevitable that conspiracy theories would abound after his death.

Mr Trump, in fact, retweeted one on the day Epstein died containing a video along with the hashtags #ClintonBodyCount and #ClintonCrimefamily.

A man calling himself Rod "Epstein Didn't Kill Himself" Webber unsuccessfully tried to register as a presidential candidate. ( Reuters: Mike Segar )

These conspiracy theories have taken on new life three months after the event, following the release of a hot mic video showing US ABC News anchor Amy Robach complaining the broadcaster would not let her report on Epstein three years earlier.

Internet meme-makers, particularly those with a right-wing bent, quickly commandeered the speculation and turned it into a running gag.

A typical Jeffrey Epstein meme. ( Supplied: Know your meme )

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Former Navy SEAL Mike Ritland appeared on Fox News to talk about his work with retired military dogs, but managed to sneak in a reference to Epstein, marking the meme's crossover into the mainstream.

He told GQ he wanted to "keep [the story] in the news".

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A man calling himself Rod "Epstein didn't kill himself" Webber attempted unsuccessfully to declare his candidacy for the 2020 New Hampshire presidential primary.

He was escorted out.

Mr Gosar played coy about the tweets, retweeting the story about the coded message and commenting: "What? Epstein didn't kill himself?"

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He also responded to media inquiries with this statement to The Hill:

"All of the tweets pertained to testimony from today's hearing. Rest assured, they are substantive. Every one of them. All of them. 5 were brilliant. 1 was ok."

The first letters of each sentence spell out "AREA 51".