The congressman heading the Committee on Homeland Security has sent an angry letter accusing the FBI and Department of Justice of failing to brief lawmakers on the threat of domestic terrorism. He sent the letter just hours before 49 people were killed at New Zealand mosques and police arrested a suspect who had praised American white supremacists.

More domestic terrorism suspects were arrested in the United States over the last two federal budget years than those inspired by foreign Islamic extremists, The Washington Post reported last week, citing figures from the FBI. Most domestic terrorism suspects are right-wing extremists. But domestic terrorism is not a crime under federal law, so suspects are charged with weapon violations and other crimes.

Rep. Bennie Thompson (D-Miss.) on Wednesday sent his third letter to the FBI and the Justice Department demanding a committee briefing on the “evolving threat of domestic terrorism” after earlier requests were ignored. “Regrettably, this is just the latest example of non-cooperation on this important issue,” Thompson wrote. He asked again for a briefing, this time for the end of March. The committee plans to hold hearings on the issue in coming months.

Thompson on Friday expressed sympathy and offered prayers to all those affected by the brutal attacks on two mosques in Christchurch.

“The terrorism in New Zealand underscores that we must not ... ignore the domestic terrorism threat,” he said in a statement. “We must all work together to counter domestic terrorism, including those who feed it and allow it to spread.”

Federal law enforcement has been criticized for focusing too much on decreasing Islamic-linked terrorism and not enough on the rise of violent right-wing extremism in the U.S. The threat is largely shielded from the public because of the lower-level charges.

An example is former Coast Guard Lt. Christopher Hasson, an avowed white nationalist arrested last month with a cache of weapons. Hasson allegedly planned to kill progressive politicians and journalists in what prosecutors have described as a domestic terrorism plot. But Hasson hasn’t been charged with terrorism, only with a series of weapon and drug crimes.

About 110 people were arrested in the 2017 budget year after being investigated for crimes inspired by foreign terrorist groups, such as ISIS; 30 of those faced terrorism charges, the Post reported. The following year, 100 were arrested and nine faced terrorism charges.

In the same time span, 150 domestic terrorism suspects were arrested the first year, and 120 the following year, according to FBI figures provided the Post. No terrorism charges were filed against any of them.

Violence by white supremacists and other right-wing extremist disciples has been rising since Barack Obama’s presidency and has surged since Donald Trump took office, according to the Post.

Early this year, the Anti-Defamation League released a report that said attackers with ties to right-wing extremist movements killed at least 50 people in the U.S. in 2018. That was nearly the total number of Americans killed by all domestic extremists.

The ADL has also reported that 71 percent of the extremist-related fatalities in the United States from 2008 to 2017 were committed by members of the far right or white-supremacist movements. Islamic extremists were responsible for 26 percent.

Some experts have pointed to Trump’s incendiary rhetoric as a cause.

“If you have politicians saying things like our nation is under attack, that there are these marauding bands of immigrants coming into the country, that plays into this right-wing narrative. They begin to think it’s OK to use violence,” Gary LaFree, a criminologist at the University of Maryland told the Post.

Trump said Friday, when asked about the Christchurch massacre: “I don’t really” see a rise in white nationalism. “I think it’s a small group of people.”