In recent weeks, conspiracy theories claiming that a slain Democratic National Committee (DNC) staffer provided thousands of stolen emails to WikiLeaks have reignited. Speculation, previously relegated to internet messageboards, has now moved into mainstream politics.

Unfounded rumours about 27-year-old Seth Rich, killed on 10 July 2016 while walking home in a popular Washington DC neighbourhood, have existed for months. His death came roughly two weeks before WikiLeaks published a batch of 20,000 emails from inside the DNC.

Within the past week, high-profile figures including 2012 presidential candidate Newt Gingrich, WikiLeaks founder Julian Assange and internet entrepreneur Kim Dotcom have all fuelled the conspiracies.

Gingrich, speaking on 21 May, sparked online speculation by saying Rich may have been "assasinated". These are the same rumours the Rich family has consistently worked to refute since last year.

The swell in mainstream coverage of the conspiracy theories was the result of a Fox5 report, published on 15 May, claiming Rich was involved in the leak.

The Fox5 article quoted a private investigator called Rod Wheeler who said Rich had been in direct contact with WikiLeaks before his death, and had likely sent the website tens of thousands of DNC emails.

Wheeler provided no evidence to back up his claims and, three days later, was handed a cease-and-desist letter by a lawyer representing the Rich family, the Washington Post reported.

"Your improper and unauthorised statements, many of which are false and have no basis in fact, have also injured the memory and reputation of Seth Rich and have defamed and injured the reputation of the members of the family,' " lawyer Joseph Ingrisano wrote in the letter.

Family spokesperson Brad Bauman, who also does public relations for Democratic Party candidates, said: "Anyone who continues to push this fake news story after it was so thoroughly debunked is proving to the world they have a transparent political agenda or are a sociopath."

Police in Washington DC have said the case remains under investigation. The city's deputy mayor for public safety, Kevin Donahue, told News4 there is "no WikiLeaks connection".

He elaborated: "This is a robbery that ended tragically. That's bad enough for our city, and I think it is irresponsible to conflate this into something that doesn't connect to anything that the detectives have found." A police spokesperson said investigators are working to "bring closure to the case".

This failed to halt the spread of speculation.

Newt Gingrich
US politician Newt Gingrich recently spoke about Rich's murder Reuters/Mark Kauzlarich

As noted, during an interview on Fox and Friends, Gingrich gave credence to the conspiracy theory by claiming Rich was potentially killed for releasing information.

"We have this very strange story here of this young man who worked for the DNC who was apparently assassinated at four in the morning having given WikiLeaks something like 23,000 – I'm sorry, 53,000 – emails and 17,000 attachments," he said, again without evidence.

"Nobody's investigating that, and what does that tell you about what was going on, because it turns out it wasn't the Russians, it was this young guy who, I suspect, who was disgusted by the corruption of the [DNC]," he added.

Yet Gingrich is far from the only one referencing the unsolved case of Seth Rich.

On 20 May, German-Finnish entrepreneur Kim Dotcom claimed via Twitter: "I knew Seth Rich. I know he was the @WikiLeaks source. I was involved." He said a statement would be issued on Tuesday (23 May) but – at least at the time of writing – provided no evidence of the alleged links.

The day prior to Dotcom's claim, the Russian embassy in the UK spread the unfounded conspiracy theory online. "WikiLeaks informer Seth Rich murdered in US but MSM was so busy accusing Russian hackers to take notice," it posted in a tweet to its 56,000 followers.

Most recently, Assange tweeted: "WikiLeaks has never disclosed a source. Sources sometimes talk to other parties but identities never emerge from WikiLeaks. #SethRich." Last year the whistle-blowing platform offered a $20,000 (£15,340) reward for information about Rich's death.

In an interview on Dutch television in 2016 Assange refused to name the source of the DNC emails – yet played coy when asked about the rumours about Rich. "Whistle-blowers go to significant efforts to get us material and often very significant risks," he said at the time.

US intelligence sources and multiple cybersecurity firms believe WikiLeaks obtained the leaked emails from Russian intelligence as part of a widespread campaign to disrupt the 2016 presidential election and help elect Donald Trump to the White House – a claim Assange has denied.

"We assess with high confidence that the GRU relayed material it acquired from the DNC and senior Democratic officials to WikiLeaks. Moscow most likely chose WikiLeaks because of its self-proclaimed reputation for authenticity," stated a US intelligence report released in January 2017.

Fox5 has since backtracked on its initial report.

The Rich family later said in a statement: "We have been approached with no emails and only learned about this when contacted by the press.

"Even if tomorrow, an email was found, it is not a high enough bar of evidence to prove any interactions as emails can be altered and we've seen that those interested in pushing conspiracies will stop at nothing to do so.

"We are a family who is committed to facts, not fake evidence that surfaces every few months to fill the void and distract law enforcement and the general public from finding Seth's murderers."

Fox News host Sean Hannity, reacting to the claims made by Kim Dotcom, tweeted: "Congress, investigate Seth Rich Murder! @JulianAssange made comments u need to listen to! If Seth was wiki source, no Trump/Russia collusion." He later added: "Do you believe the 'robbery' story?"

At the time of writing, there remains no solid evidence linking Rich to WikiLeaks.