(CNN) — The one question we all desperately want answered may have gone to the grave with Aaron Alexis: Why?
Why did he park at the Washington Navy Yard on Monday, walk into Building 197, perch himself on an overlook above the atrium and open fire? The bullets that rained down killed 12 people and wounded eight others.
But that’s not the only missing puzzle piece. Investigators are painstakingly trying to piece together the motive, the means and the method.
“No piece of information is too small,” Valerie Parlave of the FBI said Monday night. “We are looking to learn everything we can about his recent movements, his contacts and associates.”
For now, here’s what we know and what we don’t know.
What we know: The shooting rampage ended with the death of Alexis, 34.
What we don’t know: How Alexis died. Authorities say he was killed after an encounter with security. We’ve yet to learn the details.