I understand, but its a line of inquiry they some news outlets have been suggesting that are being looked into. If this was an Islamic fundamentalist, I'd have imagine them being jumped upon to announce it was them.
And yes, it is close to the McVeigh incident.
This is looking more like a extreme right wing anti government group.
The day marks the anniversary of the opening of the revolutionary war, it's also federal income tax return day. Media would look more towards Islamic fundamentalists than an anti government nut job.
YouTube
EDIT: first...
They have sniffer dogs at a lot of high-profile events, this doesn't mean they knew anything at all. Given the recent shootings, I'd suspect a larger police presence would have been justified.
P.S Mises & Hayek > Friedman.