A federal prosecutor in Texas says the bloodshed in El Paso on Saturday was an act of “domestic terrorism.” That’s an important statement of federal law enforcement priorities, a commentator said Monday, even though the accused gunman will likely stand trial for murder, not terrorism.

Despite the terrifying nature of mass shootings, like the weekend killings of 22 in El Paso and nine in Dayton, Ohio, and the slaying of three people and wounding of 13 at the Gilroy Garlic Festival on July 28, no one has ever been charged with terrorism for lethal acts on U.S. soil that were unrelated to a foreign organization.

Even Timothy McVeigh, whose revenge-fueled bombing of a federal building in Oklahoma City in 1995 killed 168 people, was tried, convicted and executed for murder and use of weapons of mass destruction, not terrorism.

But under Justice Department policy, “it matters less what statute somebody is prosecuted under than how the case is investigated,” said Michael German, a former FBI agent who now is an analyst with the Brennan Center for Justice at New York University.

And he said the statement by U.S. Attorney John Bash of Texas on Sunday after the arrest of 21-year-old Patrick Crusius — whose manifesto called the shootings “a response to the Hispanic invasion of Texas” — signaled that the El Paso case “would be opened as a domestic terror investigation.”

That matters for two reasons, German said: Terrorism cases are the department’s No. 1 priority, in comparison with hate crimes, which rank fifth on the list. And terror investigations are broad-ranging, “seeking information about who might have been involved, who provided support to the person, any existing remnants of the organization that continue to pose a threat to the public.”

By contrast, he said, the Justice Department’s investigation of the neo-Nazi who barreled his car into a group of counter-protesters in Charlottesville, Va., in 2017, killing 32-year-old Heather Heyer, was a civil rights probe focusing on the intent of the driver and not the white-supremacist group that organized the event. The department responded after then-Attorney General Jeff Sessions backed away from his initial assessment that the attack fit “the definition of domestic terrorism.”

The driver, James Fields, was convicted of hate crimes in federal court and of murder in state court. He was sentenced to life in prison in both courts.

The USA Patriot Act, passed after the Sept. 11, 2001, terrorist attacks, defined domestic terrorism in the same way that an earlier law had identified international terrorism: criminal acts that endanger human life and are intended to intimidate or coerce either a civilian population or government policy through kidnapping, assassination or mass destruction.

The only difference is that international terrorism must take place outside the United States or must “transcend national boundaries,” a somewhat imprecise term that has been interpreted to cover domestic acts related to international terrorists. For example, analysts said the husband and wife who killed 14 people and wounded 22 in San Bernardino in December 2015 might well have been charged with international terrorism had they survived, because, although native-born, they were supporters of an overseas Islamic terror group.

It is a crime under U.S. law, punishable by up to life in prison, to provide “material support” to a terrorist organization. The FBI has identified more than 60 such groups, all based abroad.

By contrast, said Mary McCord, a Georgetown University law professor and former Justice Department official under President Barack Obama, gunman Robert Bowers, who killed 11 worshipers at a synagogue in Pittsburgh last year, was not charged, and could not have been charged, as a terrorist.

“Bowers is just as morally deserving of the ‘terrorist’ label as Islamic extremists who engage in acts of violence to intimidate and coerce,” McCord said in an online essay in Lawfare. She said the law should be changed to define a new crime of domestic terrorism.

The American Civil Liberties Union has cautioned that such a law could violate freedom of speech by penalizing people for their views. Critics have noted that between 2004 and 2008, the FBI designated “eco-terrorism,” not racism, as the leading domestic terrorist threat.

German said the U.S. government has not identified any domestic organizations as terrorist groups covered by the ban on “material support” because “Americans have a First Amendment right to associate with whom they choose.”

But McCord said the government did not have to go that far, and could prosecute someone under current law who provided support for a domestic terrorist attack that used bombs, which as a weapon of mass destruction opens the possibility of a terror charge. And German cited the case of two white supremacists who were caught in an FBI sting in New York in 2012 — a purported plot to construct a weapon that would spew deadly radiation into mosques — and were sentenced to prison for domestic terrorism.

Passage of any new laws will be difficult in the current Congress.

Sen. Dick Durbin, D-Ill., renewed his plea Monday for action on his ambitiously titled Domestic Terrorism Prevention Act, which would actually require only annual government reports on the threat of domestic terrorism, training programs and creation of a task force to look into white supremacy in the armed forces. The bill, which has 19 Democratic co-sponsors, including Sen. Kamala Harris of California, is languishing in the Republican-controlled Senate Judiciary Committee.

“White supremacy is the most dangerous form of domestic terrorism threatening our nation,” Durbin said in a Twitter posting. “If we aren’t willing to confront this threat as such, these attacks will not stop.”

Bob Egelko is a San Francisco Chronicle staff writer. Email: begelko@sfchronicle.com Twitter: @BobEgelko