(CNN)The arduous search for a missing technology executive and five others feared dead after a suspicious fire destroyed a mansion in Annapolis, Maryland, could take days, fire officials said Tuesday. 

The 16,000-square-foot waterfront house belonged to executive Don Pyle, chief operating officer for ScienceLogic, company spokesman Antonio Piraino said. 

Pyle was believed to have been at home with his wife, Sandy, and four grandchildren. 

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

"Your looking at five standard houses put together," he said. "This is more of 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." 

Pyle had not been heard from on Monday, and his colleagues at ScienceLogic were "hoping for a miracle," CNN affiliate WJLA-TV in Washington reported. 

By midday Tuesday, fire officials had not been able to search the still-burning ruins, Howarth said. Heavy equipment is being moved in over the next 12 hours to aid in the search for victims and clues -- a process that could take days. 

"We have some very unique challenges with this house," Howarth said. "The construction of the house contained a lot of very heavy materials. We're looking at some steel beams that weigh in the area of 7 tons." 
Who owned the house?
What type of house is it?
How large is it?
Did it have a cellar?
Did it have an attic?
Who else lived in the house?
How many days had passed since the fire?
Had they begun to search the house yet?
Why?
Any other reason?
Who was heading the search?
What's his rank?
What state was the house located in?
What county?
Had anyone gotten any communications from Pyle?
Who is ScienceLogic's representative?
Who is the COO?
What was his wife Sandy's occupation?
How many are thought to be dead?
Don Pyle
The 16,000-square-foot waterfront house belonged to executive Don Pyle
Waterfront
waterfront house
16,000-square-foot
he 16,000-square-foot
Yes
 collapsed into the basement
unknown
unknown
Pyle's wife and four grandchildren
his wife, Sandy, and four grandchildren
unknown
unknown
No
By midday Tuesday, fire officials had not been able to search the still-burning ruins
Parts were still burning
 still-burning ruins
Waiting for equipment
Heavy equipment is being moved in over the next 12 hours to aid in the search for victims and clues
Robert Howarth
 Robert Howarth, who is leading the investigation
Captain
Capt. Robert Howarth
Maryland
mansion in Annapolis, Maryland
Anne Arundel
Anne Arundel County
No
Pyle had not been heard from on Monday
Antonio Piraino
company spokesman Antonio Piraino
Don Pyle
Don Pyle, chief operating officer for ScienceLogic
unknown
unknown
Six
technology executive and five others feared dead