Most people think of the attack on Columbine High School in 1999 as a school shooting. Sue Klebold thinks of it as her son Dylan's murder-suicide. She's written a new book and says she hopes the insight it provides outweighs the risk of re-traumatizing victims' families. Klebold answers a question she's faced for years: How could her son have planned the attack without her knowing? And she says she'll never know if she could have prevented her son's actions, but she does wish she could've done some things differently.