I'm telling you, the Oklahoma City Memorial Museum should serve as the absolute model for some eventual 9/11 museum. With one major quibble, the way they present the narrative, the artifacts and the testimonies of the bombing couldn't be better handled.
You can get as much or as little info as you want--either follow the main path of the exhibit to get the basic throughline, or detour into many side areas which let you look deeper into the issues and experiences. For instance, one side section explores the 200 terrorist incidents in the U.S. in the 10 years before Oklahoma City (not just the first WTC attack, but also abortion clinic bombings, animal rights activist sabotage, etc.), with interactive computers giving you in-depth info about each incident. Or the computers that let you search out and view lengthy video interviews with survivors, rescuers and family members.
One especially sensitive area that I thought they handled just right is info about the capture, trial and execution of Timothy McVeigh. Many people, wanting only to remember and mourn the victims, would object to seeing McVeigh represented here, so most McVeigh info is shunted off into side paths, clearly separated from the rest of the exhibit, so you can choose to see it or not. Very smart layout.
The only thing missing that I thought needed to be there was any discussion of McVeigh's reasons for doing it. I understand why many people would object to the idea of giving him any kind of mouthpiece to justify mass murder, but I think it's too important an issue to avoid (in a "those who don't know history are doomed to repeat it" sense). Without understanding the thinking that allows someone to blow up 160-something strangers, you're not going to know how to stop the next one. The way the museum allowed you to avoid the other McVeigh material shows they could have kept it offstage.
I gave a pretty full description of the museum a year ago in Loog's
168 Seconds of Silence (OKC Revisited) thread if you want more portentuous blather.