LOS ANGELES — The FBI is opening a domestic terrorism investigation into the shooting that killed three people, including two children, at a popular California food festival, a law enforcement official said Tuesday.

Nineteen-year-old gunman Santino William Legan fatally shot three people with a Romanian-made AK-47-style rifle before turning the gun on himself on July 28 at the popular Gilroy Garlic Festival. Thirteen others were injured.

The official was not authorized to discuss the investigation before a news conference and spoke on the condition of anonymity.

The person could not immediately give specifics about why the FBI is opening a domestic terrorism case.

Authorities have not yet disclosed a possible motive in the case.

A separate mass shooting that killed 22 people at a crowded El Paso, Texas, store over the weekend is also being handled as a domestic terrorism case.

The FBI’s move in Gilroy came as Keyla Salazar’s family was set to hold a funeral mass Tuesday for the 13-year-old in San Jose.

Federal investigators have fewer tools and legal powers at their disposal in domestic terrorism cases than they do if they are up against someone tied to an international organization such as the Islamic State or al-Qaida.

Law enforcement officials conducting international terrorism investigations, for instance, can get a secret surveillance warrant to monitor the communications of a person they think may be an agent of a foreign power or terror group.

Similarly, the U.S. criminal code makes it a crime for anyone to lend material support to designated foreign terror organizations, including the Islamic State and al-Qaida, even if the investigation doesn’t involve accusations of violence.

There’s no domestic counterpart to that material support statute, meaning federal prosecutors must rely on hate crimes laws, weapons charges and other approaches that may not carry the terrorism label. Mere membership in, or support for, a white supremacist organization is not illegal.