LINDEN, Calif. – A high school student who hid undercover to catch a thief says she was shocked to find that the culprit was a teacher.

Justine Betti, a sophomore at Linden High School, told News 10 that students had become suspicious after noticing items missing from their backpacks in gym class all year.

Betti decided to hide in a locker in hopes of catching the thief, and she was successful. She said she observed the teacher rummaging through student backbacks.

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“After all the kids left she stayed in there and went through people’s backpacks,” Betti said. “I saw her take money and then I told people and nobody believed me.”

But Betti refused to let it go.

“Something needed to be done. Like, that’s not ok,” Betti told reporters.

On February 13, Betti hid in a locker for the second time, armed with a cell phone camera and another camera propped up in a second locker.

“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.

Both cameras show the teacher going through backpacks, according to news sources. At one point, the teacher can be seen taking money from a pink backpack.

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“I was like, oh my God, I can’t believe I got this on video and I couldn’t believe that I got it and I kept watching it over and over,” she said.

Betti and several friends showed the video to the school principal who promised to take action.

“He said that he’ll investigate it and he told us to delete the video but I had already sent it to my dad.”

The unidentified teacher has been placed on administrative leave and both the school district and the San Joaquin County Sheriff’s Department are investigating, reports News 10.

As of yet, no criminal charges have been filed.

Several students said the teacher has been at the school for 30 years and is well liked.

Linden sophomore Kellie Martinez said she has mixed feelings about the allegations.

“Makes you feel like your privacy was invaded, but you know, you can’t help but feel bad for her, either… she was a great teacher,” said Martinez.

Betti said had a difficult time deciding to make the footage public, but said her classmates supported her decision.

“We feel like we did the right thing, but it’s still kind of hard,” Betti said.