Smith told the Washington Post's Erik Wemple on Saturday that Buzzfeed's internal investigation included an exhaustive review of more than 500 of Johnson's posts for the site.
Forty-one of Johnson's posts were tainted with lifted text and a lack of proper attribution, a discovery that dismayed Smith.
“I was hoping what I’d find was a handful of instances from beginning and then somebody who had figured it out,” Smith told Wemple.
The Twitter pair, known as @blippoblappo and @crushingbort, followed up that effort on Friday by surfacing six more instances of plagiarism in Johnson's archives, forcing Smith to confront the issue.
"There are serious instances of plagiarism in this post," Smith told TPM in an email on Friday. "We're reviewing Benny's work."
Smith announced the firing in an internal memo to Buzzfeed staff on Friday evening.
"Tonight’s decision is not a knee-jerk response to outside criticism, though we are genuinely grateful to the people who helped point out instances of plagiarism," Smith said in the memo, which was provided to TPM by a Buzzfeed spokesperson. "Nor is it meant as a personal condemnation: Benny at his best is a creative force, and we wish him the best."
Smith also posted a mea culpa to Buzzfeed readers shortly before midnight. The post has since been updated to include a list of the 41 posts with "plagiarism and attribution issues."
Each of those posts now includes an editor's note indicating that the copied text has been removed.