The Justice Department is facing mounting pressure to file federal hate-crime charges in the Atlanta spa shootings, setting up a test for the Biden administration in managing public expectations in a case that experts said illustrates the difficulty in prosecuting and winning a conviction.

In the decade since Congress most recently expanded hate-crime protections in 2009, the number of referrals to federal prosecutors under all five existing federal statutes was significantly lower than it had been over the previous 25 years, according to data compiled by Syracuse University’s Transactional Records Access Clearinghouse (TRAC) program.

And of the nearly 2,000 cases investigators referred through mid-2019, only about 15 percent resulted in prosecutions, the study found.

Among the cases that went forward were high-profile attacks by Dylann Roof, convicted of 33 federal hate crimes for gunning down nine black parishioners in Charleston, S.C., in 2015; Robert Gregory Bowers, indicted on 44 federal counts for the shooting deaths of 11 worshipers at a Pittsburgh synagogue in 2018; and James Alex Fields Jr., sentenced to life in prison after pleading guilty to federal hate crimes for driving a car into a crowd and killing a counterprotester at a white-supremacist rally in Charlottesville in 2019.

But experts said law enforcement officials’ handling of the killings of eight people, including six women of Asian descent, at three spas in the Atlanta area last week has demonstrated flaws in how federal and local authorities are collaborating on the investigation of whether the alleged shooter, Robert Aaron Long, 21, was motivated by race or gender or national origin.

Authorities said Long, who is White, told them that he was seeking to eliminate sexual temptation in carrying out the killings. A sheriff’s deputy in Cherokee County, north of Atlanta, where one of the spas was located, appeared to discount potential hate-crime charges, saying Long was having a “really bad day” when he attacked the Asian-owned businesses at which police said he had been a patron. The deputy was reassigned from the case amid public outrage at his remarks.

Federal investigators also appear to have leaked information to news organizations, including the Associated Press, which reported over the weekend that the inquiry has yet to turn up evidence that would constitute a hate crime.

“The disconnect is that law enforcement seemed to downplay bias, particularly racial and ethnic bias, as a motivation for a crime very quickly,” said former FBI agent Michael German, a fellow at the Brennan Center for Justice who has written critically of how his former employer investigates white supremacy and hate crimes.

German said the Justice Department has long followed a policy of deferring to local authorities in handling potential hate-crime cases. But he said states have inconsistent and weak laws that local prosecutors often choose not to pursue because they fear that doing so could complicate efforts to win a conviction.

“Whether substantial evidence can prove it beyond a reasonable doubt, the fact that law enforcement would forfeit those claims in public statements is terribly inappropriate,” German said. He added that doing so “reinforces the belief among many communities who are targeted in these kind of crimes that police don’t care as much when they’re the victims of crime rather than the suspects.”

U.S. officials said the FBI is assisting local authorities in the investigation, while lawyers in the Justice Department’s civil rights division are involved in determining whether the crime meets federal hate-crime statutes. Police in Georgia have charged Long with eight counts of murder.

The officials cautioned that such an assessment can be a slow and arduous process, and that it is expected to go well beyond what Long told local police about his motives. Investigators will seek to examine Long’s emails and social media, and interview his family and friends. They could potentially convene a grand jury to hear evidence.

Yet Asian American leaders have begun explicitly calling for hate-crime charges, arguing that Long clearly knew his targets would be Asian women, some who immigrated from Korea, given his familiarity with the spas.

Rep. Judy Chu (D-Calif.), chair of the Congressional Asian Pacific American Caucus, noted that Long drove more than 25 miles between the businesses, suggesting that he could have attacked other establishments had he not been motivated to attack a specific set of workers.

A White handyman working at one of the spas and a White female customer also were killed in the shootings.

“I feel very, very strongly that this is a hate crime,” Chu said. “The law may have its own standards that need to be met. But we don’t have to wait for the shooter to tell us he was targeting a specific race and gender. His actions clearly show what’s on his mind.”

Since President Lyndon B. Johnson signed the first hate-crime legislation in 1968, lawmakers have approved five federal statutes covering race, sex, religion and national origin. The most recent came in 2009 when Congress passed the Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act, which expanded protections to cover gender, sexual orientation and disabilities.

The Syracuse University study found that, despite the beefed-up legal tool kit, prosecutors pursued a diminishing number of cases under the Shepard-Byrd Act. Under the Trump administration, the government brought six cases in both 2017 and 2018 and four in the first three quarters of 2019, according to the study.

Federal officials said investigating hate crimes is challenging because although some perpetrators make their intentions clear through manifestos or deliver threats or slurs while carrying out the attacks, others say little about their motivations.

Jeannine Bell, a law professor at Indiana University who has studied hate crimes, criticized authorities for leaking information in the middle of an investigation that cast doubt on hate-crime charges. Doing so “creates the idea that it’s impossible to find” such evidence, she said, when in fact “perps don’t spend all sorts of time hiding their motives.”

In her research, Bell added, police told her that evidence “is there if you’re willing to look for it. That’s one of the biggest issues with prosecutors and the cult of difficulty around hate-crime cases. They’re difficult because you have to do something that you don’t normally have to do.”

In Georgia, the state supreme court in 2004 struck down a hate-crimes law passed four years earlier, calling it too vague and too broad. Last year, months after Ahmaud Arbery, a Black man, was fatally shot by White assailants while jogging, Gov. Brian Kemp (R) signed a hate-crimes provision that would impose up to an additional year in prison and a fine of up to $5,000 for one of five misdemeanor offenses, and at least two years in prison for a felony offense.

German, the former FBI agent, said prosecutors at times choose to forgo hate-crime charges because they think they would make it more difficult to win a conviction and are not worth the effort, especially in a felony case involving murder, which already includes severe punishments. He said states and municipalities, many without sufficient funding and training, do not adequately track hate crimes.

The Atlanta case “highlights the failure of the Justice Department’s policy of deferring on investigations to state and local authorities,” German said.

The mounting scrutiny comes as the agency remains without several top aides to Attorney General Merrick Garland, whom the Senate confirmed two weeks ago. President Biden’s nominees to serve as Garland’s two deputies, Lisa Monaco and Vanita Gupta, are awaiting a confirmation vote, while Kristen Clarke, seeking to head the Justice Department’s civil rights division, is awaiting a confirmation hearing.

But Justin Levitt, a professor at Loyola Law School who served as a civil rights lawyer in the Obama administration, said career lawyers in the department will be motivated to carry out a thorough hate-crimes investigation.

Levitt said that Asian American leaders are justified in calling the case a hate crime that has frightened the local community. By contrast, he said, “DOJ is there not to decide whether this is or is not a hate crime, but whether the facts can establish beyond a reasonable doubt whether this is a hate crime — which is different. These can be the kinds of cases that leave a community more distraught if they do not get what they feel is the right intuitive answer.”