One of the two teens behind the San Diego mosque shooting walked away from a mental health facility the day before carrying out Monday’s deadly attack, sources said.

Caleb Vazquez, 18, left the Park Mental Health Treatment Center the morning before he and 17-year-old Cain Clark killed three people at an Islamic center, law enforcement sources told The Post.

Vazquez had previously been subject to a firearms restraining order after police conducted a welfare check at his home in Chula Vista last year. The visit was prompted by a 2025 911 call reporting his disturbing social media posts.

Clark’s mother also called 911 on the morning of the shooting after he left home with guns that were kept in the house.

Despite both teenagers having been flagged to authorities, they were still able to drive to the Islamic Center of San Diego, where they killed three people before fleeing into a nearby neighborhood. The pair later took their own lives inside their getaway car.

The attackers left behind a shocking, hate-filled manifesto praising Adolf Hitler and numerous other mass murderers. The document contained scattered derogatory and racist views targeting Muslims, Jews, gay people, and others. It also expressed their desire to instigate an “all-out race war” aimed at triggering the collapse of society.

Authorities said the pair were “radicalized online.” They wore Nazi symbols and had etched racist statements into their gear. Law enforcement officials noted at a Tuesday press conference that the suspects “did not discriminate on who they hated.” More than 30 guns and a crossbow were recovered in connection with the case.

The three victims were identified as Mansour Kaziha, Nader Awad, and security guard Amin Abdullah. Abdullah was praised for his actions in helping to prevent further casualties.

“We do believe the security guard was able to help at least minimize the situation to the front area of the mosque,” San Diego police chief Scott Wahl said.