A fire protection engineer testifying for the defense in Christie Michelle Scott's capital murder trial told jurors Monday that prosecution witnesses erred when they said the fire that killed Scott's 6-year-old son Mason began on a bed.

Scott, 30, is accused of starting the Aug. 16 fire at her home on Signore Drive in Russellville. Her trial is now in its fourth week.

Douglas Carpenter, an owner of Maryland-based Combustion Science and Engineering, began an hourlong PowerPoint presentation Monday by scoffing at testimony from prosecution witnesses who have testified the fire began on or around a bed used by Scott's younger son, Noah. The youths shared a bedroom.

"The fire could only have started inside the television cabinet," Carpenter said, noting that he based his finding on the high levels of carbon monoxide found in Mason Scott's blood. "A fire started on the bed would not provide the extremely high levels of carbon monoxide found in the blood of the victim."

Carpenter testified he believes the fire smoldered for a prolonged period inside the television cabinet before producing so much heat that it ignited other furniture in the room, including the beds. He said as the fire smoldered, it produced massive quantities of carbon monoxide.

Carpenter told jurors that if the fire had began on the bed, the child would have died from burns before inhaling enough smoke to raise his carboxihemoglobin level - the amount of carbon monoxide in his blood - to more than 90 percent as found during an autopsy.

Carpenter testified the television cabinet acted as a room-within-a-room that initially contained the fire until it reached the flash point, causing the room to explode in flames.

His testimony contradicts that of prosecution witness Dana Lee, a fire investigator for the state Bureau of Alcohol, Tobacco, Firearms and Explosives, who testified he quickly ruled out the area around the television as the source of the fire because it was the least damaged part of the bedroom. Lee said books and paper stored in the cabinet survived the fire with little damage. Lee was among the witnesses who testified the fire began in the area of Noah Scott's bed.

Carpenter said Mason Scott's cause of death is not consistent with a fire that started on a bed.

"The fire could not have started on the bed since the victim would have died from heat exposure and not smoke inhalation," Carpenter said.

Dr. Emily Ward, a state medical examiner who performed the autopsy on Mason Scott, testified for the prosecution that the child died of a combination of smoke inhalation and thermal burns.

During cross-examination by Franklin District Attorney Joey Rushing, Carpenter confirmed he is being paid $300 per hour for his work on the Scott case and could earn more than $20,000 for his investigation and testimony. Carpenter also said he did not visit the burned home and based his findings largely on evidence provided by defense attorneys.

While being questioned by Rushing, Carpenter said he was not aware the beds in the room where Mason Scott died had a storage area in their base. When Rushing asked him if the drawers in the storage area for the beds could have acted as a room-within-a-room and allowed the fire to smolder before spreading to other areas of the bedroom, Carpenter replied, "I didn't see any competent ignition source under there."

Prosecution investigators were unable to determine how the bed was ignited.

Carpenter could not say what might have ignited the television cabinet. He suspects it was the television, which contained a DVD player and video cassette recorder.

Ray Franco, an electrical engineer from Mississippi who testified for the prosecution, said the television could not have caused the fire because many of its electrical components escaped the fire unharmed. He said if the fire had begun in the television, it would have sustained extensive internal fire damage.

Dennis Sherer can be reached at 740-5746 or dennis.sherer@TimesDaily.com.