shot that struck one of the gunman

A teenage girl from North Carolina was indicted Monday for allegedly aiding and abetting two teenage gunmen who killed three people in a mass shooting at the Islamic Center of San Diego in May, officials said.

Sarah Lindsay Santiago, 17, was indicted in Forsyth County on three counts of murder and a count of conspiracy after a multi-agency investigation found evidence she worked with the two teenage shooters to record and disseminate a livestream of the attack, District Attorney Jim O'Neill said.

Prosecutors said the teenage girl also sent the gunmen the hate-filled patches they wore during the attack and also published their manifesto afterward. She will be tried as an adult due to the terrorism-related nature of the crime.

The teenage girl was arrested a week prior to a grand jury indictment because law enforcement "didn’t know what she was capable of," O'Neill said. "She didn’t have to be in California; she is in our jurisdiction and today, a grand jury indicted her and held her responsible for her actions leading up to that disastrous day in May for the people of California."

Two teenage gunmen dressed in camouflage opened fire on May 18 at the mosque in the Clairemont neighborhood of San Diego before shooting themselves in a car nearby.

Had they not been slowed by security guard Amin Abdullah, mosque caretaker Mansour Kaziha and neighbor Nadir Awad — who were killed outside the Islamic Center — they may have gone on to kill many more, authorities said.

According to O’Neill, Abdullah — a father of eight and caregiver to his father — grabbed his gun and injured one of the two shooters. It likely prevented the shooters from advancing on the Islamic school next door, which had 140 students sheltering in place.

“Their plan that day was to commit mass murders, not only at the mosque, but to follow-up at a local Jewish temple,” O’Neill said, adding their final stop was to target Black students at a local high school.

The indictment states that the shooters planned to attack the Kehilat Ariel Messianic Synagogue, just 1.5 miles away, off Clairemont Mesa Boulevard. But, instead of carrying out the additional attacks, the two shooters took their own lives.

New details were released on Monday involving the San Diego mosque shooting, including how a North Carolina teen took part. According to the investigation, the shooters also planned an attack on a local Jewish temple and a high school. NBC 7's Dave Summer reports.

FBI Special Agent in Charge Reid Davis said the teenage girl had multiple opportunities to report the shooting before it happened.

"When someone has credible knowledge that a crime is going to be planned or going to be committed, particularly an act of violence, the law requires you to come forward," Davis said. "The failure to do so must have consequences."

O'Neill said the attack was believed to be the first to be "ideologically-motivated" in a century, and he urged parents to pay attention to what their kids are doing online.

"This underground subculture of hate, they listen to each other, they talk to each other on coded platforms," O'Neill said. "It radicalizes one another to the point where they carry out these horrific crimes of violence and murder."

The Forsyth County District Attorney's office worked with the FBI joint terrorism task forces of both Charlotte and San Diego, and with San Diego and Winston-Salem police departments to bring the case against the 17-year-old. San Diego County District Attorney Summer Stephan's office was aware of the prosecution and was there to support shooting victims.

A teenage girl from North Carolina was indicted Monday for allegedly aiding and abetting two teenage gunmen who killed three people in a mass shooting at the Islamic Center of San Diego in May, officials said. NBC 7 has more.

As part of the investigation, San Diego federal agents and local law enforcement have conducted more than 30 search warrants.

17-year-old Sarah Santiago is charged with three counts of first-degree murder and conspiracy. 

Santiago is expected to appear in a North Carolina court Sept. 21.

The Islamic Center was not able to provide comment on Monday.

This story originally appeared on NBCSanDiego.com.