An 18-year-old has been arrested after detectives uncovered his alleged plot to shoot up a California high school.

Carlos Barajas Ramirez was arrested at his home in Hollister and booked into the San Benito County Jail on suspicion of publishing threats to commit a school shooting at Hollister High School, according to the Hollister Police department.

The alarm was first raised on September 27 when the Northern California Regional Intelligence Centre alerted Hollister police to reports of an individual attempting to buy a firearm and planning an attack at the high school.

Working with the FBI, detectives traced the suspect’s digital trail after learning he had shared operational plans and “radical ideation” with others online.

Investigators interviewed witnesses who had been in contact with the suspect, uncovering messages detailing an alleged mass shooting plot before using account metadata to identify Barajas Ramirez and his location.

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Detectives and officers subsequently went to Ramirez’s home on October 13, where an interview and investigation determined he had actively planned to carry out the attack.

Police have not stated whether Ramirez had obtained a firearm prior to his arrest or whether he had direct ties to the school.

The department acknowledged it had collaborated quietly with school administrators throughout the probe to avoid alerting the suspect or jeopardizing community safety.

Dr Shawn Tennenbaum, superintendent of the San Benito High School District, praised the police intervention, noting that rapid guidance from law enforcement had been “instrumental to ensuring a safe environment for all”.

Authorities have said there is no active danger to students or staff.