One of the deranged 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 killing three people at an Islamic center with 17-year-old Cain Clark, law enforcement sources told The Post.

Vazquez also had a firearms restraining order issued against him after police conducted a welfare check at his home in Chula Vista last year, according to the sources.

The visit was in response to a 2025 911 call alerting authorities to his disturbing social media posts.

Clark also had a 911 call about him — placed by his mother on the morning of the shooting after he left home with guns that were in the house.

Though both teens had been flagged to authorities, they still managed to drive to the Islamic Center of San Diego and kill three people before fleeing into the nearby neighborhood.

They later took their own lives.

This is a developing story. Please check back for updates.