The man accused of setting off a small explosion last month that rattled nerves because of its proximity to a Colorado NAACP office says he was in a rage over his financial problems and was actually targeting his accountant, according to court documents filed Friday.

Thaddeus Murphy, 44, told federal agents that he made the pipe bomb out of a shotgun shell and fireworks fuses, the records said.

He said he was angry because the accountant wouldn't return his phone calls or give him back his tax records. It was unclear whether Murphy knew that the accountant, Steve DeHaven, died in June in Mesa, Arizona.

DeHaven pleaded guilty in 2010 to filing false tax returns and was released from federal prison in April 2013.

A sign for an accountant's business was still on the wall of the building, but it has been closed for 20 years, according to the president of the Colorado Springs chapter of the NAACP. The NAACP, which has been at the site since 1985, and a barbershop are the only tenants in the building.

Henry D. Allen Jr., president of the local NAACP chapter, expressed skepticism Friday about the accountant version of the story, but he would not say whether he believed his organization was the target.

"He targeted somebody in this building, and in my estimate it was not the tax people," Allen said. "Does anyone really think this guy is going to admit to this?"

Murphy has been charged with arson of a building and being a felon in possession of a firearm. DeHaven's death will not likely affect Murphy's prosecution, said Jeff Dorschner, spokesman for the U.S. attorney's office in Denver.

At a hearing Friday in Colorado Springs, U.S. Magistrate Judge Michael Hegarty ordered him held without bond pending another hearing next week. Murphy, wearing a white T-shirt, said nothing. He will be appointed a federal public defender.

Dorschner said investigators determined the bombing was not an act of terrorism. But, he added, "We're also continuing our investigation to determine whether that confession is true."

On Friday afternoon, Murphy's weathered pickup truck and trailer still sat outside the duplex where he lives on a winding street of modest apartment buildings in northern Colorado Springs. No one answered the door at his apartment.

Nobody was hurt in the Jan. 6 explosion adjacent to a wall of Mr. G's Hair Design Studios, a barber shop that also shares the building with the NAACP in a mostly residential neighborhood.

The crude device caused minor damage, failing to ignite a canister of gasoline set next to it. Even if the canister had ignited, the damage likely would have been minimal, the FBI said at the time.

Still, the explosion gained widespread attention due to its closeness to the nation's oldest civil rights organization, and the FBI investigated it as a possible hate crime.

National NAACP President and CEO Cornell William Brooks said his organization appreciates local and federal authorities' swift efforts in arresting and charging a suspect.

"We seek a continued investigation into the motive of the alleged suspect, and we look forward to the culmination of his criminal trial," he said in a statement. "We will remain vigilant as we continue fighting for civil and human rights in Colorado Springs and throughout the country."

Murphy told investigators he made the pipe bomb in his garage the night before the blast, using instructions he found online and materials from his work as a carpenter, according to court records.

Murphy believed the accountant intentionally destroyed his tax records, and he told investigators he "flipped out" because of his financial problems, the documents show. He said he wanted to send the accountant a warning.

"Murphy admitted the rationale for the pipe bomb was rage," the documents say. According to court records, Murphy owed state taxes.

Investigators searched his house and found at least seven firearms, which he is barred from having because he is a convicted felon. They also found a pack of road flares with one missing, a hobby fuse and 3 ½ pounds of commercially available explosive.

Witnesses told investigators they saw a white Ford pickup near the scene of the blast.

A Colorado Springs police detective spotted a matching vehicle Feb. 10, which led authorities to Murphy. They watched him for several days before arresting him Thursday, according to the documents.

Among other evidence, Murphy's cellphone records showed he had been close to the crime scene, and authorities found dog hair inside the pipe bomb that matched a brown pit bull living in Murphy's home, the documents show.

Court records show Murphy's criminal history includes a felony theft conviction for which he was sentenced to five years in prison in 2009.