A California high school student who hid in a locker to catch a thief who's been stealing stuff from her classmates' backpacks during Phys Ed was shocked to discover the perp was none other than her own teacher.

"After all the kids left she stayed in there and went through people's backpacks," Justine Betti said of the veteran educator who has been at Linden High School for 30 years. "I saw her take money and then I told people and nobody believed me."

Justine went back in the locker again, this time with two cell phones pointed at the scene of the crime.

"I didn't want to believe that she would do something like that because she was so nice, but then she did it," the teenager told News 10.

With proof in hand, Justine and a few fellow students went to alert the 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," she said.

Despite what appears to be an attempted cover-up — one that appears to have been entirely glossed over by the media thus far — the teacher was eventually placed on administrative leave, possibly after the video came to the attention of local authorities.

Both the school district and the San Joaquin County Sheriff's are said to be investigating the crime.

Students described the teacher as "great," and even Justine said she had a hard time turning her in. "She was so nice," she said. "Like I saw it and I would never believe it."

[screengrab via KXTV]