Story highlights Witness says man fled "just driving normal like it was a normal day"

No one was injured, but blast leaves some shaken in Colorado Springs

NAACP branch president: "Apparently we have gotten someone's attention"

(CNN) The FBI is investigating an explosion outside a local NAACP chapter in Colorado.

A makeshift bomb, or improvised explosive device, detonated Tuesday morning but failed to ignite a gasoline can placed alongside it. No one was injured, but the incident left some shaken in Colorado Springs.

"All of a sudden I heard this big boom," one witness told CNN affiliate KDVR-TV in Denver. "There was smoke everywhere; the building on the side was burnt."

The witness continued: "Whoever did it took off right away though. That's all I heard and it was scary."

The FBI's Denver office said it's looking for a balding man, about 40, who was seen leaving the scene in a white pickup with a missing or covered license plate.

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