SAN LORENZO — Three students have been detained by sheriff’s deputies at Arroyo High School after reports of a handgun prompted a school lockdown on Friday.

Officials placed Arroyo High School on lockdown Friday after reports of a student armed with a handgun.

At approximately 2:30 p.m. on Friday, Alameda County Sheriff’s deputies locked down Arroyo High School in the 15700 block of Lorenzo Avenue after reports of a student in school armed with a handgun.

“We were able to isolate that student to a particular classroom and we were able to enter that classroom and detain the student without incident and find a loaded handgun,” said Sheriff’s Sgt. Ray Kelly.

Two other students were also detained by sheriff’s deputies, who are looking into the two as associates, Kelly said.

It is not known why the student came to school with a handgun.

The lockdown was lifted close to 4 p.m.

The incident comes amidst a heightened, tense environment where both false alarms and real threats have been reported.

Nearby in Hayward, Tennyson High School was shut down briefly during lunch time after threatening graffiti was found at the school. Last week, Impact Academy in Hayward was shut down for the same type of threat. The student was eventually tracked down and faces discipline, police said.

“This is a national thing. It keeps happening,” said Hayward police Sgt. John Racette. “It’s unfortunate that people are crying wolf, but it’s a sign of the times. From our perspective it’s worth it.”

At 5:23 p.m., the Martinez Unified School District sent a letter to parents informing them that at an unspecified time in the afternoon, the school was on lockdown for an unspecified amount of time after the words “Shoot every kid” was found written on the bathroom wall of John Swett Elementary.

School administrators said they found the student who wrote the bathroom on the wall and judged that the threat was not credible.

The Martinez Police Department was unable to confirm any details other than an incident occurred around 2 p.m. Law enforcement officials referred all questions concerning the incident to the school district.