Napa Police released additional information Tuesday about a 14-year-old male River Middle School student’s threat to conduct mass shootings at River school or Vintage High School.

On Dec. 31, when local schools were closed for the Christmas holiday, a teenager told police that a fellow student was plotting to create mass casualties at one of two Napa secondary schools, police said. The suspect was arrested Jan. 2 after police searched two Napa homes associated with him.

No weapons were recovered during these searches. The teenager appeared to have been in the early stages of planning a possible attack, according to Chief Robert Plummer.

Officers searched the suspect’s computers, social media history, cellphone texts, internet history and notes. The student wanted to execute a Columbine High School-style attack, Plummer said.

Plummer said he would not elaborate further on what was found because that information could identify people who came forward to talk to police.

“Based on investigations, planning was becoming more and more aggressive,” he said.

Police alerted the public of this threat in a press release sent by the department late Monday. Officers do not believe there is a current threat to any Napa Valley Unified School District students.

The department will not name the teenager because he is a minor. He remains in custody after being arrested on suspicion of making criminal threats and dissuading a witness who wanted to report his plans, police said.

Police say the teenager threatened to kill the tipster after that person said they would tell police and parents. The student provided officers with evidence of those threats and others against other district students, according to the release.

Napa police and school district officials lauded the tipster for coming forward.

Investigators have interviewed students and other witnesses, according to the release.

Plummer, who was sworn in as the police chief on July 30, said he was aware of two other threats related to school shootings since he assumed his role. Both of those turned out to be hoaxes, he said.

Local parents took to social media to complain about the timing of the department’s press release, which came the night after students’ return to school from winter break. The school district said in a Tuesday morning press release that the investigation continued into Monday afternoon.

“I understand their concerns, I understand their anxieties,” Plummer said. “Had there been an immediate threat to anyone at the schools or the community, we would have absolutely pushed out information sooner.”

Things appeared normal at the River Middle and Vintage High campuses Tuesday around noon. A whiteboard propped outside of River Middle’s front doors read “Welcome Back!”

The campuses remained open and accessible to the public, and there did not appear to be additional security or law enforcement officers stationed nearby.

Elizabeth Emmett, spokesperson for the school district, said counselors were available Tuesday for any students or staff who wanted to talk.

Shooting threats occur occasionally, she said, but it’s unusual that police deem a threat credible.

“When you’re dealing with 17,000 kids, you get instances where students say things,” Emmett said.

The only shooting in the district’s history occurred during a science class at Silverado Middle School in May 1992, according to Emmett. One student’s arm was wounded and another student was grazed by a bullet that passed through his shirt, near his chest. The eighth grader had complained of being bullied.

In the 1992 incident, the shooter had told several fellow students that he intended to kill somebody, but they didn’t believe him and did not notify authorities.

Schools already have procedures and frequently practice drills to prepare for such events, Emmett said. The district will likely review existing policies to ensure everyone knows their role, she said.

Emmett noted that Napa Valley voters passed Measure H in June 2016 and approved the district’s request to increase its debt by issuing $270 million in bonds. The school board approved in August 2016 plans to put about $5 million of that amount toward school safety purchases such as fencing, alarms and cameras during the first phase of improvements between 2016 and 2019.

Superintendent Rosanna Mucetti wrote in a statement released Tuesday morning that the district had been in constant contact with Napa police throughout the incident, and agreed that information should not be released to parents before school Monday for fear it could jeopardize the investigation.

“We informed our River, Vintage and Harvest Middle School families at our very earliest, prudent opportunity, given the law enforcement realities,” Mucetti wrote in the statement.

The district was planning a meeting for parents at Harvest Middle and River Middle at 6 p.m. Tuesday in the cafeteria, Emmett said.

Napa police will hold a public forum on Feb. 6 on school safety, Plummer said. The location has not yet been selected, but officers will discuss the balancing act between maintaining the integrity of an investigation and releasing information to the public.

Plummer encouraged the public to stay vigilant and call 911 or the department’s non-emergency line at 707-257-9223 — depending on the severity of an incident — if they have information to share with police. Tips can be reported anonymously and students may reach out to school resource officers on campus.

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Public Safety Reporter

Courtney Teague is the Napa Valley Register public safety reporter. She can be reached at 707-256-2221. You can follow her reporting on Twitter and Facebook, or send her anonymous tip at: tinyurl.com/anonymous-tipbox-courtney.