The move contrasted with some of Burr's public comments on the outbreak, including a Feb. 7 op-ed he co-authored, detailing the federal government's preparedness.
The North Carolina Republican said in a statement Friday that he "relied solely on public news reports" and that he followed "CNBC's daily health and science reporting out of its Asia bureaus at the time."
In 2012, Congress made it illegal for members to profit financially from inside information they receive. Burr was one of only three senators to vote against that measure.
Burr said he understands "the assumption many could make in hindsight" and that he spoke Friday morning with the Senate Ethics committee chairman and asked "him to open a complete review of the matter with full transparency."
Common Cause North Carolina said there should be three investigations: one from Senate Ethics, one by the U.S. Department of Justice and one from the Securities and Exchange Commission. Common Cause state director Bob Phillips said Senate Ethics inquiries have "proven to be meaningless, by and large, in the past."
The North Carolina Democratic Party called on Burr to resign Friday morning, before the senator's announcement.
"It does not pass the smell test whatsoever," party Chairman Wayne Goodwin said. "This is a time of accountability, and people need to have faith and trust in their leaders."
Fox News' Tucker Carlson, a right-wing media personality known to have President Donald Trump's ear, called Thursday night for Burr to explain his trades or resign and await criminal prosecution.
“There is no greater moral crime than betraying your country in a time of crisis,” Carlson said during his national nightly show. "Maybe there’s an honest explanation for what he did. If there is, then he should share it with the rest of us immediately. Otherwise, he must resign from the Senate and face prosecution for insider trading."
News of the stock dump came the same day NPR reported on a recording it was given of a Feb. 27 meeting Burr had with representatives from a number of North Carolina businesses, during which he gave a dire assessment of the outbreak.
"There's one thing that I can tell you about this: It is much more aggressive in its transmission than anything that we have seen in recent history," Burr said in the recording. "It is probably more akin to the 1918 [flu] pandemic."
At the time, Trump was downplaying coronavirus fears, though other government officials were informing the public of how serious the situation might become.
North Carolina's other U.S. senator, Thom Tillis, said via Twitter Friday that Burr "owes North Carolinians an explanation."
"His self-referral to the Ethics Committee for their review is appropriate, there needs to be a professional and bipartisan inquiry into this matter, which the Ethics Committee can provide," Tillis said.
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