Fairfax County investigators said yesterday that the woman found dead with her two daughters this week in their West Springfield house apparently helped her children kill themselves before she took her life.

The statement, by prosecutor Robert F. Horan Jr., offered new insight into how Chun Shin, 36, and her daughters Aera, 13, and Jeira, 9, jumped to their deaths from a piano stool with bed sheets tied around their necks.

Horan said that his belief that the mother may have assisted her daughters in taking their lives was reinforced by the finding of identical knots in the sheets. The knots probably were tied by the mother, the prosecutor said.

"It's a rather unusual knot," he said. "A slipknot, modified. They were all tied exactly the same way."

All three deaths, discovered by a family friend Tuesday night, have been ruled suicides caused by asphyxiation, according to the Northern Virginia medical examiner's office.

Dr. Frances Field, an assistant medical examiner, said that the office does not try to estimate the time of death in such cases, especially when there is a relatively short time between discovery of the bodies and when the persons were last known to be alive.

Chun Shin and her children, who police said may have been despondent over the separation of Shin and her husband, were buried yesterday in Springfield, not far from their house, where they were found Tuesday hanging in the upstairs hallway.

"There's still a lot of grief," said Jane Y. Crim, principal of West Springfield Elementary School, where Jeira was a fourth grader. "We're still in that very tender stage of trying to comprehend it."

"The children's deaths, that's really hard to understand," said Laura Falkenstrom, a Korean employe of the Fairfax County school system who once taught English to one of the Shin girls. "It's mind-boggling."

Falkenstrom said family members, friends and the classmates, teachers and principals of the girls attended the "very simple, low-key" services at a Springfield funeral home, which were largely conducted in Korean.

Chun Shin, who moved to the United States with her family about six years ago, was known as extremely hard-working by her coworkers at Jerry's Barber Shop. Her children were considered model students. Her husband Sun Shin, 35, who left the house last weekend in what police described as a domestic dispute, ran an aluminum siding business out of the house.

Sun Shin will be needing your comfort, the ministers told the assembled family and friends, according to Falkenstrom. "At times he cried uncontrollably," she said.