I believe that there were several different things that were contributing factors to why Kipland Kinkel killed both his parents, and later two of his fellow peers. I do not think that there is one specific thing that can be blamed for Kip's behavior, but multiple things worked together to cause Kip's explosion.
One of the smaller reasons that effected Kip was the somewhat confusing messages that his parents gave him as a child about guns. Kip had always as a child had a fascination with guns and explosives, but according to his sister there was a absolutely no violence policy in the Kinkel household, which forced Kip to his explosives and information from other sources. On Kip's 12th birthday, his father gave in and Kip received a riffle from his father as a gift. From then on, Kip and his father would go to the back fields and do target practice. From age 12 and on Kip kept receiving guns from his father, but he also got them on his own.
When Kip's obsession with guns and explosives got extremely out of control, his father made a new rule: Kip's guns were constantly to be under lock and key, and he was only to use them under supervision. I think that this was a mistake made by the parents. They have sent him mixed signals about guns for his entire life, and locking them up may have driven Kip to purchase the stolen gun. It is the idea of wanting what you can't have, and when Kip's privileges involving guns gets taken away, that amount of anger could have been just the right amount to put him over the top. Creating the chaos at Thurston High.
School was also a struggle for Kip Kinkel. Not only academically but socially as well. In the elementary years, Kip was help back as all of his friend progressed to the second grade; leaving him behind. This was the beginning of his social problems and where he began to feel like an out cast. Later in high school, Kip was again not the most popular. He made an attempt to fit in by joining the...