Domestic terrorism-related cases increased 357% from 2013 to 2021, according to the Government Accountability Office, which urged the FBI and Department of Homeland Security to do more to combat the issue.
In 2013, there were 1,981 open domestic terrorism cases compared to the 9,049 open cases in 2021, according to statistics provided by the FBI to the GAO.
"From calendar year[s] 2010 to 2021, [DHS Intelligence and Analysis] tracked a total of 231 domestic terrorism incidents, with racially or ethnically motivated violent extremists committing the most violent incidents during the time period," the GAO report says. "More specifically, from 2013 to 2016, the total number of open domestic terrorism-related cases declined by over 400 (about 23%) but then increased by over 7,000 (about 490%) from fiscal years 2016 through 2021."
Out of 231 incidents, the GAO found that 35% were racially motivated, followed by anti-government motivations at 32% from 2010 to 2021.
Prosecutors charged 1,584 defendants in 1,255 cases in federal district court with crimes that were related to domestic terrorism from October 2010 through July 2021, the report says.
MORE: Domestic terrorism-related cases increased by more than 350% over 8 years: WatchdogThe number of plots that were disrupted grew by nearly three times, from 81 in 2014 to 456 in 2021, according to the data.
Since becoming Homeland Security secretary, Alejandro Mayorkas has focused the department's resources on combatting domestic violent extremism, which he calls one of the most persistent and lethal threats in the United States.
Deaths perpetrated by domestic terrorists also increased, the GAO found.
"The number of deaths from such incidents ranged from zero in 2011 to 32 in 2019, with 2015 and 2019 having the highest numbers of deaths," the GAO report says.
The GAO said domestic extremist attacks have "been perpetrated and promoted by a broad range of individuals and groups."
One of the core issues, the GAO said, is that the agencies track different types of information regarding domestic terrorism, but do not often share the information.
"DHS tracks classified, Law Enforcement Sensitive, For Official Use Only information and open-source information related to known offenders. The FBI, on the other hand, primarily tracks investigation information, including information reported to the FBI by state and local law enforcement agencies," the GAO said.
The agencies also did not sufficiently report "comprehensive domestic terrorism incident data in their 2021 and 2022 strategic intelligence reports," according to the report.
"In their first report pursuant to the act, issued in November 2020, the FBI and DHS provided their respective definitions and threat categories related to domestic terrorism," the report says. "However, the report did not include information on their methodologies for tracking incidents of domestic terrorism other than the FBI's description of an incident and a plot."
More support from state and local governments in reporting incidents that fall under the category of domestic extremism is needed, FBI agents interviewed by the GAO said.