Authorities on Friday released a composite sketch of the man they believe detonated an explosive near the offices of the Colorado Springs chapter of the NAACP.

The FBI and Bureau of Alcohol, Tobacco and Firearms also offered a $10,000 reward for information on Tuesday's explosion, which caused only minor damage and no injuries but rattled nerves due to its proximity to the nation's oldest civil rights organization. Federal officials say they do not know whether the NAACP was targeted but are investigating the explosion as a possible hate crime.

FBI Special Agent in Charge Thomas Ravenelle said authorities drew the sketch of a bald white man in his 40s with sunglasses based on accounts of witnesses who saw him place a device behind the building that houses the NAACP and a black-owned barbershop. The man returned to his truck and left as the device detonated.

Ravenelle said there were no threats to the NAACP in the weeks before the bombing. "Only the bomber knows why he put this there," he said.

The crude device failed to ignite a canister of gasoline placed next to it, but Ravenelle said even if it had succeeded it probably would have only caused minor damage. He said that doesn't undermine the seriousness of the crime, however.

Colorado Springs police said they were stepping up patrols in the area. If you have information about the suspect, the phone number to call is 303-425-7787.

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"This type of criminal act is unacceptable," Steve Bach, mayor of Colorado Springs, said in a statement Thursday. "I expect that law enforcement will work together to solve this crime and bring the responsible individual to justice. There is no place for this type of activity in our city."

Officials say the person of interest, seen leaving after the explosion by neighbors, may be driving a 2000 or older model, dirty, white pickup truck with paneling, a dark-colored bed liner, open tailgate and a missing or covered license plate," the FBI said, according to the Denver Post.