The 30-year-old mother was lounging in her apartment with her boyfriend when a story flashed on the television: three people found slain execution-style inside a Starbucks coffee shop near Georgetown.

As the couple watched the story unfold that July Fourth weekend in 1997, the woman's boyfriend had his own story to tell. He knew who committed the grisly crime, he told her. And she knew the killer, too, he said. A mutual friend.

A year passed before she revealed the details of the conversation to anyone. Now she wishes she had kept it to herself.

"I didn't believe him at first," the woman said in an interview with The Washington Post. "I went a whole year without saying anything because I didn't want to get caught up in it."

The woman was key to a break in the case that had stumped D.C. police and the FBI for 20 months, sources familiar with the investigation said. With her help, Carl Derek Cooper, 29, was arrested in March and charged with three counts of first-degree felony murder while armed in connection with the slayings of Starbucks employees Mary Caitrin Mahoney, 25, Emory Evans, 25, and Aaron David Goodrich, 18.

In August, Cooper was indicted on 48 counts of federal racketeering in a host of crimes, including the Starbucks slayings. Cooper is in jail awaiting trial.

"She did a lot to help the case," said a source familiar with the investigation.

Now, the woman who became a police informant said her life is in danger, and she blames D.C. police and the FBI. Although the FBI has offered to relocate her if "things got bad," she said, D.C. police have abandoned her.

Police Chief Charles H. Ramsey won't return her telephone calls, she said. A veteran detective who headed the Starbucks investigation promised to change her identity and hasn't.

"I want them to give us [her family] the protection they promised us," she said. "I risked my life, and now they won't even call me back."

Ramsey said Thursday that he did not receive phone messages from the woman and declined to respond to her accusations that the department has turned its back on her.

"I can't get into what we promised," the chief said. "The case is ongoing. It will all come out at the trial," which is scheduled to begin April 10.

FBI spokeswoman Susan Lloyd said she couldn't discuss the "confidential nature of the informant program."

Channing Phillips, spokesman for the U.S. attorney's office, said his office also is precluded from discussing matters involving informants.

Several sources said the woman is concerned more about collecting the $100,000 reward, which can be awarded only after someone is convicted of the killings. She denied the accusation. She has received more than $1,000 from the police department's confidential fund used to pay informants, sources said.

Another informant, Eric Butera, was killed in a robbery after a failed attempt to make an undercover drug buy to elicit information for police in the Starbucks case.

Butera's mother, Terry, filed a $115 million lawsuit against the D.C. police department in U.S. District Court in Washington, alleging the department didn't take appropriate steps to protect him.

It was a steamy July evening in 1998 when the Prince George's County woman was sitting with her mother watching "America's Most Wanted." A segment about the search for the killer in the Starbucks triple homicide grabbed her attention.

"I know who did it," the woman sheepishly told her mother. "It's somebody I know really good."

Her mother insisted that she call the show. She did.

The call-taker asked the woman for her name, address, telephone number and what she knew about the crime.

"I told them that an acquaintance of ours went into the Starbucks and robbed it," she recalled. "I told them that he demanded the white girl [Mahoney] open the safe. She wouldn't or couldn't, and he shot her.

"The black kid [Evans] tried to help the white girl, and he was shot. The other kid [Goodrich] was killed last."

Law enforcement sources say Cooper acknowledged in written statements allegedly given to detectives that Mahoney nearly escaped, making it to the sidewalk before he caught her and wrestled her back inside. He said, though, that the gun went off when Mahoney reached for it. The rest, he said, was "like a dream."

The woman said she met Cooper several years ago through her boyfriend, with whom she is no longer involved. The three of them hung out at the boyfriend's grandparents' home playing Nintendo video games and selling crack cocaine and PCP, she said.

The woman acknowledged that she has been arrested "many times" for drugs and once for armed robbery, a case later dismissed, she said. She also said she was convicted in 1993 in Maryland for riding in a stolen car that contained a disassembled gun and was sentenced to six months in prison.

The day after she called "America's Most Wanted," two D.C. police officers came to her house. They questioned her and were convinced she could assist them. A few weeks later, they attached a listening device to her, gave her marked money and dropped her off a few blocks from the house of her boyfriend's sister near Howard University. Her assignment was to buy an ounce of cocaine and get as much information as she could about Cooper, she said.

"I kind of wanted to hurry up and get this over with, so I fabricated a story to him [the boyfriend's brother] that I wanted to rob some Jamaican friends and needed some people to help me do it," she explained. "I told him I wanted old boy who did the Starbucks killing. He said okay. The police were ecstatic then because we had it on tape."

A few months later, the woman made a second drug buy under the watchful eye of D.C. police, she said. This one was in the alley behind Cooper's house in Northeast. It was there she met her boyfriend's brother, who ordered her to throw the money on the ground. She obliged, he tossed her the drugs and drove away. She did not see Cooper, she said.

She said she later identified Cooper through a mug shot.

The woman's mother said that since Cooper's arrest, she has received anonymous phone calls asking about her daughter's whereabouts.

"I called the detective, and he told me it wasn't anything I should worry about," the mother said. "But no one usually calls my house looking for her, and if they do, they don't use her street name.

"I'm truly sorry I told her to" go to the police, the mother said. "I really am."