These thoughts are based on two things: the reporting I’m hearing so far (which, since the Boston bombing we know could potentially be inaccurate,) and my mom’s knowledge of security at the Navy Yard, because until about two years ago she worked there.
Basically, if the information we have so far is accurate, then at least one of the two or three shooters (I’ve heard both numbers) was probably military personnel or employee at the Navy Yard or something. I say this for a couple of reasons.
One, people with a military ID don’t get their cars searched when they enter the Navy Yard. Frequently civilian cars don’t either, but they can be subjected to random searches. So it would be taking a pretty big chance to try and bring in weapons just hoping you won’t be chosen for a random search at the gate.
Second, reporters so far are saying that the shootings started inside a building at the Navy Yard, on one of the upper levels. Again, getting into the building armed without a military (or I guess civilian employee) ID would be pretty much impossible. All visitors and people without those IDs have to go through metal detectors.