How did they find out he had a gun and a knife? Did he tell, or display it?
From the article.
Rueben Littlejohn, the San Diego School District’s police chief, has said that staff members at Farb Middle School said they heard Walker was keeping ammunition in locked cabinets in his classroom. He also told students and staff that he had a gun and loved firearms.
Police checked the cabinets but did not find anything improper.
Officers contacted Walker, patted him down and found a .38-caliber semi-automatic pistol with a seven-round magazine. They also found a knife with a 2½-inch blade.
he told the students and staff he had a gun and loved firearms!! no where is it written that he had a gun on him at school and does not say when the “school police’ contacted him at school or home.