Hate crime murders in the U.S. reached a 27-year high in 2018, according to data released Tuesday by the FBI. Hate crime murders totaled 24, which includes the 11 worshipers slain last year at the Tree of Life Synagogue in Pittsburgh, the deadliest anti-Semitic crime in U.S. history.

New FBI statistics show hate crimes overall were down slightly in 2018 following three years of increases. Of 16,039 law enforcement agencies who participate in the hate crime data collection program, 2,026 agencies reported 7,120 hate crime incidents involving 8,496 offenses, meaning some involved multiple criminal charges. Most of the hate-crime incidents, 7,036, were "single bias," while the rest stemmed from multiple biases. The incidents involved 8,646 victims.

The FBI reported 7,175 hate crime incidents in 2017 and 6,121 in 2016.

Daniel Elbaum, chief advocacy officer for the American Jewish Committee, said it's a positive to see slightly fewer hate crimes in 2017 than 2018, but he noted that about 110 fewer law enforcement agencies contributed data. He said it was disturbing to see a significant rise in hate crime murders.

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Elbaum and other advocates point out that hate crime statistics — submitted voluntarily by local jurisdictions to the FBI — are incomplete and don't offer a full picture of bias crimes in the country.

"It's really hard to tackle a problem until you have a handle on how large of a problem it is," Elbaum said. "Nearly every expert on hate crimes agrees it's under-reported."

Of the single-bias hate crime incidents in the 2018 data:

57.5% were motivated by a race/ethnicity/ancestry bias

20.2% were motivated by religious bias

17% were motivated by sexual-orientation bias

2.4% were motivated by gender-identity bias

2.3% were motivated by disability bias

0.7% were motivated by gender bias

Of crimes motivated by race, ethnicity or ancestry, 46.9 percent were fueled by bias against African Americans. Anti-Hispanic crimes also again rose, spiking nearly 14 percent between 2017 and 2018.

Of crimes motivated by religious bias, most of the incidents, 57.8%, were anti-Jewish, according to the FBI. Anti-Sikh crimes tripled from 20 in 2017 to 60 in 2018, and crimes motivated by disability bias also soared from 116 in 2017 to 159 in 2018.

The 24 total hate crime murders recorded were the highest since the FBI began tracking and reporting on hate crimes in 1991, according to the Anti-Defamation League (ADL).

"It is unacceptable that Jews and Jewish institutions continue to be at the center of religion-based hate crime attacks," ADL CEO Jonathan Greenblatt said in a statement. "We need to take concrete action to address and combat this significant problem."

Crimes targeting the LQBTQ community increased about 6% from 2017, and the FBI reports a significant increase in hate crimes motivated by gender identity bias. The FBI said 184 hate crime offenses in 2018 were motivated by bias against transgender or gender non-conforming people — 157 motivated by anti-transgender bias and 27 motivated by bias against gender non-conforming individuals. In 2017, 118 were anti-transgender and 13 were anti-gender non-conforming.

Xavier Persad, senior legislative counsel for the Human Rights Campaign, said the data "reminds us of the importance of the work left to be done to protect LGBTQ people," particularly transgender women of color, who the group says is most at risk for violence.

Despite the slight decrease in reported hate crimes overall, Persad said the incidents "remain unacceptably high."

"We are talking about violence against people just because of who they are," Persad said.

Advocates point out a significant gap in the FBI's data which came to light because two of the most notorious hate crimes in recent years were never reported to the government, even though they were prosecuted as hate crimes. The killing of Heather Heyer in the 2017 Charlottesville car attack as she protested the "Unite the Right" rally, and the fatal 2016 shooting of Khalid Jabara in Tulsa by a neighbor who had terrorized the victim's Lebanese family, were both left out of national hate crime statistics collected by the FBI. Proposed legislation named for the victims, the Heather Heyer and Khalid Jabara NO HATE act, would provide incentives for hate crime reporting and grants for state-run hate crime hotlines.

"A year after the most deadly assault on the American Jewish community in history and with xenophobia and racism remaining front and center in our national dialogue, this bipartisan measure is necessary legislation," Sim Singh, senior manager of policy and advocacy at the Sikh Coalition, said in a statement. "If we cannot accurately track the problem of bias-motivated incidents, we will remain inherently limited in our efforts to combat them."

In 2018, at least 85 cities with populations exceeding 100,000 residents either did not report any hate crimes or reported zero hate crimes, according to the ADL. Alabama and Wyoming reported zero hate crimes for 2018.

The Justice Department has said that efforts are underway to improve investigation and reporting of hate crimes at the state and local level, including developing comprehensive training curriculums for local law enforcement, and providing resources on a new hate crimes website.