SAN JOSE — Officers found a loaded handgun inside the classroom of a Chaboya Middle School teacher on Wednesday when they went to arrest him in connection with a strong-arm robbery, police said.

The robbery stemmed from a road rage incident reported Feb. 21 on the first block of Fourth Street, Sgt. Enrique Garcia said. The suspect, later identified as 35-year-old Charles Ha So, of San Jose, allegedly assaulted another man and forcibly took his cellphone.

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Detectives obtained a warrant for So’s arrest and the MERGE Unit, San Jose’s version of SWAT, descended on Chaboya Middle School, where So teaches an eighth-grade language arts class. Garcia said students were already done for the day and So was taken into custody without incident after being summoned to the front office.

The loaded handgun was found inside a satchel in the teacher’s classroom when officers went to retrieve his property, said Garcia, adding that it was registered to So.

It wasn’t immediately clear why So had a firearm on school property, but Garcia said, “there is no indication at this time that he was going to use that handgun against staff or students.”

So, a recent hire who passed his background check on Aug. 18, has been placed on administrative leave, said Charles Crosby, a spokesman for the Evergreen School District.

“We are beyond appalled that a teacher, even a brand-new one, would think it is remotely OK to bring a weapon into one of our schools,” said Crosby, who noted that Chaboya students participated in a nationwide walkout earlier this year to protest gun violence.

Crosby said Principal Derrick Watkins notified parents of So’s arrest in a message Wednesday night.

Anyone with information related to the case can contact Detective Sgt. Ray Vaughn at 408-277-4166.

Those wishing to remain anonymous can leave a tip with Silicon Valley Crime Stoppers at 408-947-STOP (7867) or svcrimestoppers.org. Tipsters may be eligible for a cash reward.

Check back for updates.