Supreme Court nominee Brett M. Kavanaugh during his confirmation hearing on Sept. 4. (Manuel Balce Ceneta/AP)

Andrew Manuel Crespo is a professor at Harvard Law School.

Two years ago, a federal court of appeals held that polygraph tests are “an important law enforcement tool” that can help investigators “test the credibility of witnesses” and “screen applicants” for “critical” government positions. The judge who wrote that opinion: Brett M. Kavanaugh. 

Last week, the Senate Judiciary Committee asked Kavanaugh whether he would be willing to take a polygraph test regarding the multiple sexual assault allegations he faces as he seeks a seat on the Supreme Court. Considering such a request himself, Kavanaugh departed from his prior judicial opinion and told the Senate that polygraphs are “not reliable.” But still, when pressed by Sen. Kamala D. Harris (D-Calif.) about taking one, Kavanaugh ultimately said, “I’ll do whatever the committee wants.”

The committee has now asked the FBI to investigate the allegations. As part of that investigation, Kavanaugh should heed his own words and agree to undergo a polygraph test administered by the FBI, which could shed substantial light on the accusations he faces.

As President Trump has acknowledged, those allegations are supported by “credible” and “compelling” evidence, presented to the Senate last week by Christine Blasey Ford. The president is right about Ford’s testimony. I have represented multiple people accused of sexual assault. Some of them, I believe, were falsely accused. Others, I believe, were guilty. But Ford was as credible and compelling a witness as I have seen. In a criminal trial, a jury could lawfully return a guilty verdict based on testimony such as hers, even without further corroboration. Indeed, many people are in prison today based solely on the credible and compelling testimony of sexual assault survivors.

Ford’s account, moreover, bears many of the essential hallmarks that prosecutors look for when determining whether to file criminal charges against an alleged assailant. She has vivid, detailed memories of the central event. She also describes inconvenient details that someone fabricating the assault would likely omit — including her claim that Kavanaugh’s close friend Mark Judge is a witness who can confirm or dispute her account. And, importantly, she told multiple people about the assault several years ago, long before Kavanaugh was a Supreme Court nominee.

She also took a polygraph test, administered by a retired FBI agent, which showed no signs of deception in her claim that she was sexually assaulted and that Kavanaugh was the person who attacked her. To be sure, polygraphs, like many investigative tools, are not perfect. They can sometimes produce false results, particularly if the person being tested has been trained to evade them. But as the National Research Council observes, the test is most accurate when used to examine a specific set of events — such as specific allegations of sexual assault or other specific instances of past behavior (which is how the test was used when questioning Ford, and how it would be used to question Kavanaugh). In that setting, the National Research Council concludes that “polygraph tests can discriminate lying from truth-telling at rates well above chance,” so long as the subject is “untrained in countermeasures.”

Given this general reliability, the Justice Department has used polygraph tests to identify “deceptive responses to specific questions” for more than 70 years. In fact, the FBI routinely uses polygraphs when conducting both criminal investigations and background checks. In a 2006 report, the FBI reported administering nearly 10,000 tests a year and about 7,000 during background checks alone. More generally, according to a more recent McClatchy report, the federal government requires polygraphs of “more than 70,000 job applicants and employees across the country each year to determine whether they’re trustworthy enough to get security clearances or jobs.”

As the FBI has explained to Congress, the government relies on polygraphs so heavily because multiple federal agencies consider the test “to be an effective and acceptable screening tool.” Indeed, it is not just the federal government that thinks the test is reliable. Criminal defense attorneys also frequently administer polygraphs to their own clients before those clients testify.

Kavanaugh’s attorneys apparently did not ask him to take a polygraph in the week leading up to his Senate testimony. But the FBI can and should ask him to submit to one now, as it frequently does when conducting background checks of people seeking important government positions. Such an examination would probe Kavanaugh’s denials of sexual misconduct in detail, and would also examine other features of his recent testimony that may call his credibility into question.

In short, to quote Kavanaugh’s prior judicial opinion, a polygraph would “test the credibility” of what he has told the Senate and the nation thus far, and thereby give him an important opportunity to bolster his denials. And for those who see the current controversy as a case of “he said, she said,” a professionally administered FBI polygraph could offer important additional information about who said the truth.