Hindenburg Research, which last week called Nikola (NASDAQ:NKLA) "an intricate fraud built on dozens of lies" on Tuesday returned with a follow-up report arguing the electric truck maker's recent actions back up its initial claims.

On Sept. 10, Hindenburg published a report claiming that Nikola has greatly overstated its battery and fuel cell technologies. Nikola responded to those allegations, and has threatened to take legal action against the noted short-seller. The Securities and Exchange Commission is currently taking a look at Hindenburg's concerns, a step Nikola said it welcomes as a way to bring clarity.

A Nikola truck prototype.

Image source: Nikola.

Nikola shares traded down 5% on Tuesday morning after Hindenburg, in a new post, said Nikola's response "has holes big enough to roll a truck through." The firm said that its initial report contained 53 questions about Nikola's business, but that Nikola had only answered 10 of those questions so far in its response.

"Of those 10 responses, the company debunked nothing," Hindenburg wrote. "Instead it either confirmed or sidestepped virtually everything we wrote about, and in some cases raised new unanswered questions." 

Among the allegations that Hindenburg claimed to be confirmed was Nikola's admission that a video that appeared to show its semi-truck powering itself was really only showing the truck roll down a hill.

If nothing else, the back and forth creates a lot of uncertainty for investors. Electric vehicle stocks were already volatile prior to the allegations, with investors increasingly excited about the potential for new technologies to disrupt the automotive industry

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