The massacre at the mosque was only the beginning: the teenagers planned to attack a synagogue as well

Sarah Lindsay Santiago, a resident of Winston-Salem, North Carolina, was arrested on Sunday and charged with three counts of first-degree murder and conspiracy to commit first-degree murder.

Although she is 17, a grand jury decided to try her as an adult. She will be tried in an adult court, and her identity is permitted for publication. If convicted, she could be sentenced to life imprisonment without the possibility of parole. She is being held without bail.

Forsyth County District Attorney Jim O'Neill revealed the plan to attack the synagogue at a briefing he held. According to authorities, the two shooters also planned to attack a school where most of the students are Black. In a manifesto they left behind, words of hatred were found against Jews, Muslims, Black people, and other groups.

The massacre took place on May 18 at the Islamic Center of San Diego. 18-year-old Caleb Vasquez and 17-year-old Kane Clark stormed the place while about 140 children were in the school operating on the premises. The three murdered are security guard Amin Abdallah (51), custodian Mansour Kaziha (78), and Nadir Awad (57), the husband of one of the teachers. According to authorities, the three managed to stop the attackers and prevent a much larger number of casualties.

Fled the mosque - and committed suicide in the car

After the massacre, the two shooters fled the scene and later took their own lives inside their car. In the vehicle and in materials they left behind, inscriptions and messages of white supremacy were found, as well as a manifesto in which they tried to justify their actions.

According to the indictment, Santiago agreed with Vasquez and Clark even before the massacre that she would record the live broadcast of the attack, distribute the footage online, and then publish their manifesto.

Investigators claim that she even purchased for Vasquez a patch with the "Black Sun" symbol - a symbol originating from the Nazi era and later adopted by neo-Nazi organizations - and sent it to him so he would wear it during the shooting.

Millions of messages were checked

The investigation is being conducted in cooperation with the FBI's Joint Terrorism Task Forces in San Diego and North Carolina, the San Diego and Winston-Salem police departments, and the Forsyth County Sheriff's Office. Investigators collected testimonies from more than a hundred people, executed about 30 search warrants, and checked about four million messages.

Prosecutor O'Neill said that investigators identified an "underground subculture" online, where young people radicalize each other and encourage the commission of acts of violence.

According to him, only three people watched the original live broadcast. Authorities have not yet stated whether the other two viewers were identified and whether proceedings will be taken against them.

Santiago's attorney, Ellen Dorasamy, told the AP agency that her client is innocent and that she has not yet received the investigation materials. Santiago's trial is expected to take place in North Carolina.