Hours before a fatal fire at a southwest Missouri group home, a maintenance man trying to fix a furnace shorted the electrical wiring running through the attic where investigators believe the fire started, according to documents released Tuesday.

The investigation report by the state fire marshal's office did not pinpoint an exact cause of the Nov. 27 fire that killed 10 and injured dozens at the Anderson Guest House. But it listed an electrical short or overload in the attic as a possible cause.

The information about the maintenance man's work on Nov. 26 was included in the fire marshal's investigation report released to The Associated Press under a state open-records law request. The report labels the investigation as non-criminal.

Documents show that the maintenance man told a fire marshal's investigator he had used pliers to stick a wire into an open outlet in the furnace room in order to trip the breaker while he worked on the furnace.

Deputy chief fire marshal Bill Zieres told the AP on Tuesday that the short-circuit would cause an unusual amount of heat to move through the wires, which in this case ran through the attic. Investigators have said previously that they found evidence of improper wiring elsewhere in the attic. Poor wiring would be more susceptible to starting a fire when overloaded by a short-circuit, Zieres said.

"That is among the things that could cause damage, but there's no way for anybody to prove it at this point because of the extent of the fire damage in that area" of the attic, Zieres said.

The fire marshal's documents identified the maintenance man as David Forrester, of Carl Junction. Reached by telephone Tuesday, Misty Forrester said that her husband did not have any comment.

The investigation report said Forrester intentionally tripped the breaker because he did not know which switch in the circuit-breaker box controlled the furnace. Asked why he short-circuited the electrical system instead of simply unplugging the furnace as he had a furnace in another part of the building, "He said, `I don't know, didn't even think about it,"' said the interview report by fire marshal's investigator Randy Sweet.

Forrester told another employee, after shutting the circuit breaker off, that both the facility's furnaces had problems and that he would get parts and return to fix them the next morning, Nov. 27.

The fire was reported about 1 a.m. on Nov. 27.

"The possibility of an electrical short in the attic could not be eliminated," said a final on-scene report by fire marshal's investigator Bruce Thurlo. "The only probable cause for the fire ignition in the attic area was electrical wiring."

The investigation report did eliminate other causes. Contrary to some initial witness reports, there was no evidence of an explosion. Nor was there any evidence the furnace ignited the fire, or that it was intentionally set, the report said.

Earlier this month, documents obtained by The Associated Press indicated that several months before the fire, state regulators had sought to take away the home operator's license because of concerns that it had failed to pay taxes and faced potential financial insolvency.

Instead of denying licenses to Joplin River of Life Ministries Inc., the Missouri Department of Health and Senior Services granted a series of temporary permits that allowed its home for the mentally ill and disabled to remain open.

Last week, the Missouri attorney general sued the operators, claiming the business had been secretly and illegally run by a man previously convicted in a Medicare and Medicaid fraud scheme.