Linden High School sophomore Justine Betti said students had been noticing items were missing from their backpacks after gym class all year. She decided to hide in a locker to try to determine the culprit, KXTV-TV, Sacramento, Calif., reported Tuesday.
"After all the kids left she stayed in there and went through people's backpacks," Justine said, adding, "I saw her take money and then I told people and nobody believed me."
At that point, Justine decided to use the video function on her mobile phone to record the teacher, whose name was not reported, in the act. Betti showed the video to the school's principal.
"He said that he'll investigate it and he told us to delete the video but I had already sent it to my dad," Betti said.
The Linden School District and the San Joaquin County Sheriff's Department are investigating the teacher, KXTV reported.
Betti and other students told the news station they felt bad about showing the principal the video because they liked the teacher.
"I didn't want to believe that she would do something like that because she was so nice, but then she did it," Betti said.