Tech executive Don Pyle, his wife Sandy and four of their visiting grandchildren had been unaccounted for and believed inside the home when the fire broke out at 3:30 a.m. Monday, according to relatives and neighbors.
The remains were sent to Baltimore for autopsy and identification, Anne Arundel County Fire Capt. Russ Davies told reporters. Searchers discovered the remains with the help of dogs.
Officials are still investigating the cause of the fire at the 16,000-square-foot mansion that resembled a castle, which is now a charred stone shell.
The house was "built more like a commercial structure," Davies said today, so searching is a "time-consuming process."
"There is still a lot of work to be done," Davies said.
The fire is still being handled as a criminal investigation, officials added.
Crews started going through the wreckage at the scene today, according to ABC affiliate WJLA, a process that Bureau of Alcohol, Tobacco, Firearms and Explosives investigators said could take weeks.
Records show the house was built in 2005 with a value listed at $4.2 million, according to the Associated Press.
The four-alarm fire -- which was reported by an alarm-monitoring company and a neighbor -- may have raged, in part, because the mansion didn't have fire sprinklers, which were not required when it was built.
"We are going to sift through pieces of evidence, every piece in there, room by room, so that's going to take time," said Bill McCullem, a special agent with ATF's Baltimore Field Division.
The house collapsed as it burned, and heavy pieces of debris will need to be moved, county fire officials have said.
Grieving friends such as Will Frece, a former colleague of Don Pyle, said they can't imagine anyone wanting to hurt Pyle or his family.
"My experience working with him was a couple of the best years of my life," Frece said. "He was a terrific leader."
ABC News' Bazi Kanani, Michael S. James, Dan Good and the Associated Press contributed to this report.