The deliberately-set fire that killed an elderly Upper Malrboro couple in their home Monday was ignited in a lower-level family room with a flammable liquid, Prince George's County police reported yesterday.

Both police and county fire officials said they still had no suspects and no motive on the blaze that resulted in the death of Vance A. Hinley, 70, A retired D.C. policeman, and his wife, Catherine, 66. The Hinley's son, Thomas, 46 who was in the home at 8527 Montrose St. when the fire broke out shortly after 7 p.m., escaped with minor injuries, police said.

Mr. and Mrs. Hinley apparetnly became trapped in the portion of the home, according to fire officials; their bodies were found huddled on an upstairs floor.

Residents of the quiet neighborhood that surrounds the Hinley's home remarked yesterday on the speed with which the fire spread through the brick and feame house. "I couldn't believe the fire got so hot so fast, said Joanna Talbert, who has lived in the area 14 years.

Three neighbors went to try to help the Hinley's trying first to open a door and then, out of desperation, breaking out a window.

"It was just too hot. Flames were everywhere," said one neighbor. "If you look at the burned bushes in front of the home and the grass, you can see how hot it was." Firemen said the house was engulfed in flames by the time they arrived.

Damage to the home and its contents was estimated at $70,000.

The Hinleys were recalled as quiet people who had no apparent problems in the neighborhood. Hinley was said to have retired form the D.C. police force more than 15 years ago, was crippled and recently had suffered a heart attack.

Following autopsies performed in Baltimore yesterday, Medical Examiner Dr. Bert F. Morton said the Hinleys died as a result of .

Three firemen suffered minor injuries in fighting the blaze and smoke and inhalation were treated at Greater Southeast community Hospital.