(CNN) — A Colorado man has pleaded guilty in a January explosion outside of an NAACP chapter in Colorado Springs.

Thaddeus Cheyenne Murphy, 44, pleaded guilty to damage to a building by means of fire and explosion and felon possession of a firearm, according to a statement from the FBI. He is scheduled to be sentenced in November.

Murphy told investigators that he had placed the bomb in a bid to get back at his ex-accountant who had not returned his calls, the FBI said. No one was injured in the blast.

The local NAACP shares a building with just one other business, Mr. G’s Hair Design Studios. Also on the building was a sign that read “Income Tax” but, according to the FBI, that business had not been active for some time.

At the blast site, investigators found a metal pipe, a piece of a road flare and a gas can, which had failed to ignite.

Investigators tracked Murphy by locating his truck, which matched witness descriptions of one seen at the explosion.

A search of his truck and residence turned up several firearms, including two assault rifles, a handgun, two shotguns and a WWII-era Russian made battle rifle, the FBI said. A homemade silencer was also found, as well as leftover components from an improvised explosive device.

As a convicted felon, Murphy was not allowed to possess firearms.

Colorado Springs is about 70 miles south of Denver.