Gavin Waller, 11, has taken a few punches and some hurtful words at Ada Harris School in Cardiff. He showed 10News his backpack that he recovered after it was stolen at school Wednesday."Somebody urinated in it and left a note with some more pornographic language and other things that were really horrific," said Gavin's father, Jamie Waller. "At that point, I lost it. I said, 'I'm done.' I don't have to be Colombo to know who did it. This kid's been harassing him all year long."The note found in Gavin's backpack said: "I hope you die. I hope you go to hell. (Expletive) your family and your mom is a psycho. P.S. I (urinated) in your backpack."Waller said his son has been tormented since his first day at the school."But this is a little crazy; urinating in your backpack? The detective said in all his years of covering bullying he's never seen a case like this," said Waller.Gavin said he knows why the other kids pick on him."Because I'm different; I don't surf or skate like them, and don't play soccer. I'm like an outsider," Gavin told 10News.The Wallers say various children have bullied Gavin over the years since he transferred to the school from Arizona.Waller said that is no excuse, and on Thursday morning he told San Diego County sheriff's investigators the same bully threatened to stab Gavin with a knife after school."At that point, I was like, 'That's it, you're not going to school today. I mean, the school is supposed to provide a safe environment for my kid to learn in, that's the law and I don't feel like they're doing it," said Waller.Waller said he believes the school's principal is trying to sweep the matter under the rug. He claims the school's principal didn't want to reprimand the child bullying Gavin because it's so close to the end of the school year."I really feel like they just want to ignore the situation, because they don't want the reputation," he added. "It says to me they're not going to do anything until a kid ends up in the hospital. Then they'll take it seriously."Cardiff School Superintendent Jill Vinson told 10News the principal of Ada Harris School is fully aware of the circumstances and is in the process of conducting an investigation."We clearly don't tolerate bullying at all," she said, adding that disciplinary action would be taken if justified.Sheriff's officials confirmed an investigation is under way."We take bullying seriously," said Henry Tirado, a Crime Prevention Officer with the sheriff's department who interviewed Gavin about what happened.Tirado explained that the sheriff's department conducts anti-bullying programs at several local schools, but hasn't been asked to do the program at Ada Harris School."I'm tired of being bullied," said Gavin. "I feel depressed when I go to school, I really do, because its getting out of hand; I've been bullied so much."Vinson said the district is open to any sort of bullying program as long as the curriculum is appropriate for its students.After 10News aired Gavin's story Thursday evening, the Wallers said several classmates called Gavin to apologize.They also claimed several parents called to thank them for standing up to bullies.