(CNN) An electrical failure ignited a dry,15-foot-tall Christmas tree in a fire that destroyed an Annapolis, Maryland, mansion, killing four children and their grandparents, Anne Arundel County fire officials said Wednesday.

Technology executive Don Pyle; his wife, Sandra; and four grandchildren died in what Bureau of Alcohol, Tobacco, Firearms and Explosives agent Bill McMullan called "a tragic accident that occurred at the worst possible time while the Pyles and their grandchildren were sleeping."

"The involvement of the Christmas tree explains the heavy fire conditions," Fire Chief Allan Graves said at a news conference.

The grandchildren have been identified as Alexis (Lexi) Boone, 8; Kaitlyn (Katie) Boone, 7; Charlotte Boone, 8; and Wesley (Wes) Boone, 6. They were the children of Sandra Pyle's sons, Randy and Clint Boone.

"While the explanation that has been shared with us today does not bring solace, it does start us down the long road to acceptance," a statement Wednesday from the Boone and Pyle families said. "Our tragedy has touched many lives in many families, and, in different degrees, is shared by each of us. Our hope is that our loss will raise awareness that this tragic event could happen to any family. "

Tree cut down two months prior

The blaze started in the waterfront mansion's great room, with 19-foot ceilings and connections to living and sleeping areas. It was fed by a towering Christmas tree that was cut about two months earlier, fire officials said.

The tree was lit most of the time, officials said.

"The fuel load from the Christmas tree itself is what created the significant amount of fire and heat to cause the fire to spread as quickly as it did," Deputy Chief Scott Hoglander said.

Authorities were alerted within minutes by a fire-alarm system monitored outside the home and a neighbor's 911 call. The home, which was constructed before 2005 legislation requiring a sprinkler system, did not have the devices.

"We're very comfortable that this was an accidental fire," Graves said.

Sandy and Don Pyle died along with their four grandchildren in the fire.

The medical examiner's office positively identified the victims, officials said. Five bodies were recovered in the days after the fire; the final one on Monday.

The children were visiting their grandparents for a sleepover because January 19 was a school holiday, a family spokeswoman said.

Charlotte Boone, 8, is among the four grandchildren who died in the fire.

"We believe that life is about making memories. As we work through our pain and loss, the memories we made with our family will sustain us," the families' statement said.

Officials said they were still conducting tests to determine the exact sequence of events, but believe the fire was sparked by a faulty electrical outlet.

Smoke detectors in homes are common but fire sprinklers are not, says the Federal Emergency Management Agency. Fire sprinklers reduce the death rate by 83%, property damage by 69% and firefighter injuries by 65%.

Fires in homes are responsible for more than 80% of fire deaths in the United States, according to the agency.

Wesley (Wes) Boone, 6, died in the fire.

Christmas tree fires are three times more deadly than home fire in general, according to the National Fire Protection Association.

Local and federal officials last week secured the structure and accessed the foundation of the 16,000-square-foot house. Cadaver dogs led them to the bodies, officials said.

Authorities were initially treating the house as a crime scene. Officials said it is standard procedure for a case such as this and no evidence has been found to indicate suspicious activity.

The house belonged to Pyle, chief operating officer for ScienceLogic , and his wife, Sandra, company spokesman Antonio Piraino said.

JUST WATCHED 'Suspicious' fire engulfs mansion, 6 missing Replay More Videos ... MUST WATCH 'Suspicious' fire engulfs mansion, 6 missing 01:52

The sheer size of the structure and the fact that three-fourths of the building had collapsed into the basement, with deep piles of debris still smoldering days after the blaze, compounded the search, Anne Arundel County Fire Capt. Robert Howarth said. He led the investigation along with a team from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

"You're looking at five standard houses put together," he said last week. "This is more of a commercial fire than it is a residential fire. There are a lot of businesses that aren't 16,000 square feet. That adds to it."

Fire officials said they were alerted to the fire about 3:30 a.m. January 19. About 80 firefighters responded.

The ATF national response team responded because the fire was deemed suspicious, Howarth said.

The fire department said crews had difficulty putting out the fire because the house is secluded, apparently with no fire hydrants on the scene.

Fire crews had difficulty battling the blaze because the house is so secluded.

Photos the fire department posted on Twitter showed hoses stretched for long distances. Davies said it took hours for fire department tanker trucks and a fire boat on an adjacent creek to bring the fire under control.