Shopping mall killer's suicide note

In Omaha Neb. on satarday, 19-year-old suicidal boy shot 8people in shopping mall. he left a note and it is shown now. It says that he loves his family and friends, and he feels sorry for them to be burden. (complete sentences is on yahoo news titled "Transcription of Hawkins' suicide note") I can not understand why he did shot people if he sorry for his family and friends. the people who ware kileed have nothing related to that. This issue makes me be furious and disgusting. It is really incomprehensible.