Seven months after an 18-year-old Korean woman, Hye Ja Yi, was beaten and then stomped to death in Gaithersburg, Montgomery County police are still searching for her killer.

"We are continuing to receive leads and information from people calling in, and we are checking everything out, but so far we have nothing substantial to lead us to who did it," said Lt. James H. Elkins, commander of the Germantown investigative section.

Elkins said police have checked with the FBI, which keeps track of slayings throughout the United States, to determine if the Gaithersburg case was part of a pattern of crimes committed by a serial killer. "But this is unlike anything else in the country that has been reported to the FBI," Elkins said.

Yi was last seen at 8:50 p.m. Monday, April 29, when she stepped off the bus at a busy Gaithersburg intersection and began walking toward her home, about three-quarters of a mile away.

She never got there. Her battered, partially clothed body was found about 6:30 the next morning in a ditch behind the construction site of a Giant Food Store about two miles from her home. The girl had been sexually assaulted and then literally stomped to death, police said.

Elkins said the killer may have been someone that Yi knew, because she apparently got into a car as she walked from the bus to her home. "But it is also possible that she was forced into a car by someone she didn't know," he said.

The slaying stunned Gaithersburg High School, where Yi played piano in the school orchestra, and it shocked the close-knit Korean community and the peaceful community of Gaithersburg where the family has lived since arriving from the suburbs of Seoul in 1978.

Yi's older sister, Hyeran Yi, 22, said Friday that the family "still thinks about her . . . . We don't know who killed her . . . . It is very hard, but we have each other." Hye Ja Yi was one of four children.

Family and friends of the young woman have contributed $12,000 for a reward for information leading to the arrest of Yi's killer. Anyone with information is asked to call Crime Solvers at 301-840-2444.