Wow, Who do it?

That day the whole school in an uproar, classroom windows 7b, 7c, and 7d solved, as well as grade 8 and 9 are missing a lot of goods, including textbooks, of course there was something suspicious, would the thief is someone at school, because, schoolgirl wearing a special book the school itself.
Staying 7a and 9a class is still not stolen, then after school the children were conferred 7a class.
"How can we not stolen?" Ask Nia "Well, it was difficult, because our window-glass windows" Answer the class president "Well, what if we make a small camera?" Nuel said "It's expensive," A class treasurer. 
The children were silent all "Hey, if the camera, we can only use mobile phones" said Tina "Well how do?" Ask Lia "Ah, I can set with video call, but ... it's a little pay "Answer Tina" But that did not prevent us from theft "Larry says" I'll catch the thief "said Tina" But, what if some child care at school "said the head of the class, the class agrees, which has a handphone Ayu most handphone for small to put in the corner and made as much as possible so as not to appear. 
Finish installing mobile Ayu, they gathered at the home Nuel and enable video calls, while the six children on guard around the school with the class president, a pack of security guards fortunate to accompany them.
Not until night fell, about six o'clock, there was someone from the door, he turned over the unfinished buildings, to their surprise, the kids at home Nuel immediately contacted six children in school to ride to their classes together.
A child caught accidentally took the book left on the table ordered the teacher.
Pak security guards to secure the child immediately, while the children let go mobile Ayu, after which they handed to the teachers and principals who happened not home, the child was not able to, he can steal to stay in school, pity and headmasters provide text books provided he return all the loot. Children 7 classes also provide notebooks and stationery.
The entire school was amazed at 7a-grader, of course 7a graders also feel relieved to have found the thief.