She took the rollers out of her hair minutes after the phone rang at 3 a.m. and, despite the objections of her boyfriend, headed out the door of the East Harlem apartment she shared with her mother and brother’s family. She was alone.

The late-night excursion was not unusual for Beatrice Rivera, 33. She was known to go out late, and to disappear, sometimes for days at a time. This time, however, was different.

She failed to call her son the next morning. The week drifted by, and messages left on her cell phone went unanswered.

On Saturday a father and son riding bicycles in the Bronx noticed a garment bag on a grassy patch of land off of Pelham Parkway, about a quarter mile from Bruckner Boulevard. Inside lay the body of Rivera, naked except for some jewelry she was wearing and a plastic bag found wrapped around her head, police said. The body had been decomposing for at least two days and, as a result, medical examiners said they have not been able to determine the cause of death.

Police identified Rivera by her fingerprints, which were taken several years ago after she was arrested for allegedly assaulting another woman, Maria Maldonado, Rivera’s sister-in-law, said.

Family members described Rivera as outgoing and tough.

“She was a strong girl, and I know if someone tried to do something she’d fight,” her son’s father, Jose Angel Rios, said.

To her oldest brother, William Echevarria, 41, she would always remain his baby sister, the youngest of her mother’s six children. Originally from Puerto Rico, Maria Rivera traveled to America 35 years ago and settled in Connecticut, where Beatrice Rivera was born.

A single mother of six, Maria Rivera relied on welfare to make ends meet. When that was cut short, Mr. Echevarria – who has a different father than his slain sister – said he had to drop out of high school two weeks before graduation to get a job.

“I was like her brother and her father,” Mr. Echevarria said, his eyes welling with tears.

Most of Beatrice Rivera’s life was spent among several neighborhoods in the Bronx, where the family lived for 20 years before moving to East Harlem. In the Bronx, where many of her friends still live, she met her son’s father, who is now 34. It was in the Bronx that the young couple shared their proudest moments: becoming parents with the birth of their son, Angel, now 16, and moving into their first apartment, at Hunt’s Point. Their years together ended in 1995, when Rios was arrested for dealing drugs, he said. He spent the next eight years in prison. Beatrice Rivera moved in with her mother.

Three years ago, Beatrice Rivera received her GED, a high point in her life that led to a part-time job as a clerk at a medical office in Harlem. Another high point was a photograph taken with the pop star Marc Anthony, who grew up in her apartment building at East 101st Street.

Beatrice Rivera was known as a woman who always spoke her mind.

“She was very open, she always told the truth,” her son said.

When she received the late-night phone call, however, she said very little to the two people who were still awake at that late hour: her boyfriend, and her sister-in-law, who lived in a room next-door. Ms. Maldonado, 43, said she overheard the name “Miguel,” but when she asked where Rivera was going she received only a vague answer.

“I’m gonna go hang out with friends,” Ms. Maldonado said she was told.