Those eight words were enough to send the stock soaring — up by nearly 11 percent by the end of the day.
Musk later posted that the only thing he needed to take Tesla private was a shareholder vote.
The SEC complaint says that "Musk had not even discussed, much less confirmed, key deal terms, including price with any potential funding source."
It alleges the 47-year-old "knew or was reckless in not knowing that each of these statements was false and/or misleading because he did not have an adequate basis in fact for his assertions."
As NPR's Sasha Ingber reported:
"Musk said [later] his tweet was prompted by Saudi Arabia's sovereign wealth fund, which brought up the possibility of taking the company private. Tesla later admitted that it did not have the funding for the deal, and less than three weeks after his tweet, Musk walked back the prospect of going private.
"Short-sellers who had anticipated that Tesla's stock would fall said Musk's tweet was meant to manipulate the shares, according to the Associated Press."
In a statement on Tesla's website following the initial tweet, Musk provided an explanation for setting the stock price at $420, writing that he had calculated the price per share based on a "20% premium over the stock price following our Q2 earnings call (which had already increased by 16%). "
The court documents note the calculation resulted in a price of $419, but that Musk later admitted he had added the extra dollar — $420 — "because he had recently learned about the number's significance in marijuana culture and thought his girlfriend 'would find it funny, which admittedly is not a great reason to pick a price.' "