I had the same thought. I never saw them using the slides. Moreover when those guys from Pune Film Archive were visiting St. Martin's they said that they hadn't used the slides in a long time and these were collecting dust there. But how did the manager come to know as soon as the slides were stolen. Does he get the boxes counted every day?
When the watchman called Ronit he got his voicemail and when police called they would have gotten the same message. Then how did the police come to know that Ronit was a stident in St. Martin's? Moreover Ronit stole slides and he is the one who should be punished. Why should the matter be reported to the college?