The New York Times offers this interesting analysis of the backpack, which the author describes as an 'accessory to murder' and an invitation to extra scrutiny.

The article asks perhaps the more poignant question, what is the real catalyst for the scrutiny - the backpack itself or the color of the wearer's skin? An "olive-skinned" man wonders, "I don't know if it's the size of the pack, or the color of my skin, but I do notice, when the SWAT teams are out, they're looking at me."