Edward Y. Chen's statement to homicide detectives six years after he allegedly shot his parents and older brother to death in their Great Falls home cannot be used against him at his trial next month, a Fairfax County judge has ruled.

According to newly filed court documents, Chen, 27, told Fairfax police in March that he had just returned home with his family from Taiwan in August 1995, where he was involuntarily placed by his family in a hospital for the summer. "I bought a rifle, a hunting rifle at Kmart," Chen told the police, according to the papers. "And one night I really just lost my nerve, lost my mind and I did it . . . . I shot them . . . . My brother and my parents."

But before Chen made those statements to Fairfax homicide Detectives Steve Shillingford and John Wallace, he had said, "I don't want to talk about it." He also had asked if he could call his lawyer. Fairfax Circuit Court Judge Jonathan C. Thacher, in a ruling signed Thursday, found that "Chen's statement 'I do not want to talk about it' cannot be viewed as anything other than an invocation of his right to remain silent."

Fairfax County Commonwealth's Attorney Robert F. Horan Jr. did not return a phone call yesterday to discuss whether he would appeal the ruling.

Peter D. Greenspun, one of Chen's attorneys, said, "We felt that the law was clear, that the police had improperly obtained evidence, and that the court followed the law."

In addition to a transcribed copy of part of Chen's statement to police, prosecutors filed other documents revealing new details about the deaths of Wu-Hung Chen, 53, his wife, Yeh-Mai Chen, 52, and their older son, Raymond, 25:

* Edward Chen's former girlfriend, Vickie Henry, tipped off police to the triple homicide by dialing 911 on March 19 to report that Chen had killed his family. Several days later, at detectives' request, Henry made a recorded phone call to Chen. The contents of those calls were not disclosed.

* After his parents' bodies had lain inside their Great Falls home for nearly four years, prosecutors allege that Chen and a friend dismembered the bodies and mixed them in cement before placing the cement in duffel bags. Chen and the friend then drove the bodies to the Chesapeake Bay. The bodies have not been recovered. The friend has not been charged.

* Chen admitted that he assumed his older brother's identity in subsequent years, using his brother's power of attorney to sell the family's real estate holdings and net more than $1 million, the court papers say. Chen also drew a diagram of his parents' bedroom for detectives, showing where their bodies lay.

Chen's ex-wife, Mandy Chen, has said that Chen was upset with his parents because they didn't like her and had tried to separate them. Chen's parents lived mostly in Taiwan, but owned six houses in Northern Virginia, including one where their two sons lived. Mandy Chen testified at a preliminary hearing that Edward Chen -- then 19 years old -- shot his family to stop their interference with his life, and the young couple soon had a child and married.

They divorced in 1999, and Edward Chen began dating Vickie Henry, 30. Chen and Henry split up in the fall of 2001.

Shillingford testified that while he was moving Chen's 6-year-old daughter and another child away from the arrest, Chen asked Wallace, "Can I call my lawyer?" The detectives told him yes. Chen was then taken to police headquarters, where he was read his Miranda rights to have a lawyer and to remain silent, and he initialed each one.

Shillingford, in a discussion before he began taping, said he wanted to know why Chen had killed his family. "I don't want to talk about it," Chen told him. Shillingford asked if the subject was too painful, and Chen said it was. Shillingford said he responded, "It's been painful for a lot of people." But Chen again said, "I don't want to talk about it."

In a subsequent tape-recorded statement, Chen said he didn't want to talk about what happened in Taiwan, according to the transcript. But he then describes the killings, which he said occurred while all three family members slept in their beds.

Thacher ruled that Chen had "unambiguously and unequivocally invoked his right to counsel" by asking about calling a lawyer while at his apartment. And Shillingford's attempts to question Chen after Chen demurred "constituted interrogation," Thacher said.

EDWARD Y. CHEN