The two teens who carried out a shooting at the Islamic Center of San Diego on Monday were wallowing in a world of hate.

"These subjects did not discriminate in who they hated," said Mark Remily, special agent in charge of the FBI's San Diego Field Office, at a press conference Tuesday.  

Authorities said they believe the two teens met online and discovered they were both residents of the San Diego area before meeting in person.

The two, radicalized online, shared a hate-filled vision of the world, according to investigators. A document the FBI called a "manifesto," which has been reviewed by CBS News, appears to glorify past mass shooters and spout anti-Islamic and antisemitic rhetoric as well as racist and misogynistic speech.

A suicide note left by one of the teens indicated he was willing to die for his abhorrent cause, according to a law enforcement source familiar with the investigation.

One of the teens, 17-year-old Cain Clark, was on the wrestling team at a local high school. The other, Caleb Vazquez, was 18.

Investigators are probing evidence that indicates the teens were influenced by a litany of mass shooters, including the perpetrator of a 2019 mass shooting at a mosque in Christchurch, New Zealand, that the attacker livestreamed.

The teens filmed their own attack Monday and the gruesome 10 minute video was widely shared to a gore website where people post videos depicting violence. CBS News has previously reported on past mass shooters who have spent time on the platform.

After carrying out the attack that killed three people — including a security guard who was praised for saving countless others — the video shows Clark, wearing camouflage, fatally shooting Vazquez before taking his own life. 

The video also shows weapons and gear emblazoned with neo-Nazi insignias.

Authorities said the teens had stockpiled 30 guns and a crossbow, weapons taken from parents of one of them.

An early warning

The first warning came in around 9:40 a.m. when the mother of one of the shooters called 911. She said she worried that her son was suicidal after she discovered that multiple weapons and her vehicle had been taken. Her son, she said, was wearing camouflage.  

The information triggered a threat alert, but there was no known specific target, according to law enforcement sources.

Two hours later, the two teens opened fire at the mosque. They killed a security guard out front, then entered the facility, which houses a school where more than 100 children were in attendance. The attackers started to go door to door, but thankfully, the guard, Amin Abdullah, had already triggered a lockdown alert and the students were in another area of the building.

Then, investigators say,  the teens spotted two men in the parking lot through one of the windows. They exited the mosque to target and kill them, then jumped in their vehicle and fled, shooting out the window of the car.

A few blocks away, Clark shot his friend and himself.

Glorifying violence 

The so-called "manifesto" that investigators are also reviewing is 75 pages long and appears to be a compilation of writings that have been circulating in the darker corners of the internet for years, possibly pulled together with the help of AI. CBS News has not independently verified who created the document.

The document is filled with language associated with nihilistic violent extremism, and references "accelerationism," one of the most violent forms of white supremacist ideology that advocates for the destruction of society.

The video investigators found was posted to a website which has been on the FBI's radar amid a disturbing trend of young people engaging with what's called the "True Crime Community," or TCC, an online movement that glorifies mass shooters and encourages violence and self-harm.

A source familiar with the investigation said he believes the video was initially recorded on Discord, a popular online platform for gaming.

The source told CBS News that the video appeared to have been posted by someone using the alias "Otto." A CBS News review found that "Otto" had deleted all of their posts on the site.

A spokesperson for Discord did not immediately respond to CBS News' request for comment.