As Republican presidential front-runner Dr. Ben Carson plays defense on accounts that he was offered a full scholarship to West Point and was a youth so troubled that he once tried to stab a friend, new reports of biographical inaccuracies are coming to light.

During the aftermath of Dr. Martin Luther King Jr.’s assassination, for example, Carson — then, a junior at Detroit’s Southwestern High — claims to have heroically protected a few white students from anger-fueled attacks by hiding them in the biology lab, where he worked part time. But The Wall Street Journal could not confirm the account through interviews with a half-dozen of Carson’s classmates and his high school physics teacher. All of the students remembered the riot, but none could recall white students hiding in the biology lab.

Related: Carson Faces Scrutiny Over West Point Claim

It’s one of several biographical claims upon which Carson has relied in an effort to appeal to evangelical voters, who value the retired neurosurgeon’s personal journey from troubled youth to pious doctor. As Carson has shot to the front of the Republican presidential pack, however, parts of that narrative have been called into question.

Carson, for his part, is taking a defiant stand in hopes of portraying the scrutiny as a witch hunt by the media. During a press conference Friday evening, the usually subdued Carson appeared agitated and accused the press of not examining President Obama’s past to the same extent when he was running for the White House in 2008. Carson took another swipe at the “biased media” on Twitter Saturday, announcing that his campaign had raised $3.5 million this week in spite of the negative attention.

We the People have made 10,000 donations each day this week, raising $3.5M this week alone. Thank you biased media. -Dr. Ben Carson (@RealBenCarson) November 7, 2015

Still, the questions threaten to be a persistent thorn in the campaign’s side. In another anecdote, Carson wrote in his 1990 autobiography, “Gifted Hands,” that a Yale psychology professor had told his Perceptions 301 class their final exam papers had “inadvertently burned,” and that all 150 students would have to retake it. The new exam was much tougher, Carson wrote, and everyone besides him walked out of the class. Carson then recalled being approached by a photographer from The Yale Daily News and the professor, who Carson claimed told him the re-test was “a hoax” to see who was “the most honest student in the class.” Carson said the professor handed him a $10 bill.

No photo identifying Carson as a student ever ran in The Yale Daily News, however, according to The Wall Street Journal’s examination of archives, and no stories from that era mention a class called Perceptions 301. Furthermore, Yale Librarian Claryn Spies told The Wall Street Journal Friday that there was no psychology course by that name or class number during any of Carson’s years at the university.

Carson’s campaign did not respond to MSNBC’s request for comment.

The Wall Street Journal’s report is the latest in a series of stories that raise questions about Carson’s past, as told through his long career as an author and inspirational speaker. CNN reported this week that Carson’s childhood friends and acquaintances could not recall the White House hopeful as a violent troublemaker in his youth — certainly not one who would’ve stabbed a friend, as Carson claims in “Gifted Hands,” had the blade not miraculously broken on a belt buckle. In response, Carson went on Fox News’ “The Kelly File” Thursday and said the person he tried to stab was a close relative who did not wish to come forward.

On Friday, meanwhile, Politico dug into Carson’s account that he was “offered a full scholarship” to West Point, but decided instead to pursue a career in medicine at Yale. A spokesperson for the prestigious military academy told Politico that the school had no record of Carson even applying, let alone gaining acceptance. Carson’s campaign later admitted that he never applied to West Point, but was given an offer based off his ROTC record during an informal meeting with a school representative.

Carson told reporters during the news conference Friday outside West Palm Beach, Florida, “there is a desperation on behalf of some to try to find a way to tarnish me.”

“My job is to call you out when you’re unfair,” Carson said, “and I’m going to continue to do that.”

Carson’s fellow presidential hopefuls have offered mixed reactions over the past few days. New Jersey Gov. Chris Chris told CNN on Friday, “I’m sure Dr. Carson will answer any questions that anyone might have about his personal story and the voters will decide if that answer is good enough or not.”

Vermont Sen. Bernie Sanders said Saturday that Carson’s proposal to “abolish Medicare” is more important than decades-old biographical details.

Former Hewlett-Packard CEO Carly Fiorina dismissed the controversy in an interview set to air Sunday on NBC “Meet the Press.”

“I know Ben Carson, I know he’s a good man. …. So I think voters are focused on the issues that matter to them.” Asked whether the Carson controversy has caused her to re-examine any of her past comments, Fiorina said bluntly, “No.”

Donald Trump didn’t let Carson off the hook, posting several tweets quoting criticisms of Carson’s record.

This article first appeared on MSNBC.com.