Authorities continue to investigate the cause of an early Monday morning fire in Derwood that killed a 5-year-old boy and his mother and grandmother. The only survivor was the boy's 13-year-old brother, who was awakened by a smoke alarm about 4 a.m. and ran to a neighbor's home to call for help.

Fire chief Thomas Carr says firefighters initially struggled to enter the one-story home because the blaze was so intense. Once inside, they found 75-year-old Paula Curiel and 5-year-old Adam Sanchez in a bedroom. Forty-two-year-old Guillermina Curiel Garcia was found in the living room-dining room area.

Guillermina, also known as Gail to many, was the owner fo the Costa Alegre Restaurant on Greenbelt Road in Berwyn Heights. Monday night, the only light shining inside was the jukebox.

The 5-year-boy was taken to the hospital, where he was pronounced dead. The mother and grandmother died at the scene. The teenage boy, Oscar Sanchez, escaped with minor injuries.

"I know her boys and I am really heartbroken over her son being the only one left. It's unbelievable," said Jessida Ortega. "To be that young and to lose his mother, and his mother and his grandmother that's really sad, my sympathy goes out to him."

Officials say the fire appears to have started in the living room-dining area as a result of burning candles or an electrical short. An exact cause has not been determined. Damage is estimated at $500,000.

Authorities report the house had working smoke alarms on both floors on the home.

Montgomery County fire spokesperson Pete Piringer said this the 13th fire fatality in the county this year - about double the number of previous years.