I feel that while I certainly have nothing constructive or helpful in this tragedy- I do understand better than most that situation.
I was working at the Tacoma Mall in Tacoma, WA in November of 2005, when the "Tacoma Mall Shooting" occurred. Right around Thanksgiving time, a guy came into the mall, the wing with Santa to take pictures with and the Build-A-Bear shop mind you, and opened fire on a Sunday morning. I am thankful that I was in a different wing, but I will never forget what it's like to first of all have people come through your store saying there is a man with guns shooting people outside, and then to have the SWAT guys come into the store and tell everyone to get out (As a caveat, I will also not forget that they told us to keep working- they'd shut the big glass doors, cause that will keep out the AK rounds, and for customers to continue shopping).
I didn't know what was going on, exactly in the interim, but I did make sure to call my parents and my (at the time) boyfriend (who didn't bother to answer... good thing we're not together anymore!) and try to let them know that if they were watching tv I was okay...
I think what I remember most is the Emergency response people setting up triage points and then the big Mobile Command busses coming through. All the while just waiting, and not knowing.
We were lucky in Tacoma, our shooter didn't kill anyone. My heart goes out to those people in Omaha, and I am so sad for them.