Four weeks after the death of Alexandria businesswoman Dorothea Lane Cutts II - who was found bound and gagged in the smoke-filled basement of her Old Town town house - police say they still have no motive and no suspect in the July 29 arson-homicide.

"This is certainly one of the more unusual cases we've ever handled," said Capt. Carl Dutzman, head of the criminal investigation division. Dutzman said the police department has interviewed more than 100 friends and acquaintances of the slain Cutts with no success.

In a separate development, a $5,000 reward was offered yesterday by friends, for the arrest and conviction of Cutts' assailant. "The money has been placed in a trust fund," said Patrick Marshah, a family friend. "It's an added incentive. Hopefully, it will jolt somebody."

Marshah could not confirm who was responsible for the reward, but said it was apparently set up as a blind trust by the family's attorney in Warrenton, Louis Costello. "The family did not contribute the money," said Marshah. Costello could not be reached for comment.

Police are still awaiting comprehensive lab reports on items taken from the house several days after the homicide. "We took an awful lot of stuff from the house - bedclothes, bedding, utensils. We also picked up containers of household cleaning fluids. There is some evidence of inflammable being used," Dutzman said.

Dutzman added that a test for alcohol in Cutts' blood was negative.

According to police, three fires had been set around 5 a.m. in the lavishly restored town house. Cutts' body - clad in a nightgown - was discovered at 6:15 a.m. by firemen clearing smoke from the basement. Earlier, neighbors had reported seeing a light in Cutts' second floor bedroom. The house had been locked.

An autopsy revealed that Cutts died from smoke inhalation and police theorize that she was trying to crawl to a broken window for air.

"She came very close to surviving," said Dutzman.