The victim, Vaughn Mitchell Robinson, 48, evidently was about to do laundry Wednesday morning when the assault began.
At 8:20 a.m., she dialed the emergency 911 police number.
Reginald Roundtree, police spokesman, gave this account:
"There was a lot of screaming. She said she needed help. There was a black male in her house. He was coming after her. She was hysterical.
"He was assaulting her. She was unable to speak. You could hear the woman choking and gasping for breath. Then there was silence.
"Then somebody - we think it was the killer - said something, then hung up the phone."
Detectives said the killer might have tried to imitate his victim's voice.
The woman's terror so alarmed Cynthia Carter, 25, a police communications clerk, that she ignored routine procedures. Instead of typing the information into her computer terminal, she ran across the room to the dispatcher.
Quick, she said, get somebody on the way. This "woman is in trouble! She needs help immediately."
Police had a car on the way at 8:21 a.m., a full minute before the computer officially handled the incoming call. Officers arrived three minutes later, only to find Robinson's body.
Estelle Arwood, 18, admitted to involvement in the killing of her stepmother after being confronted by police, spokesman Angelo Bitsis said.
Arwood, who is white, had quarreled with her stepmother about dating one of the black youths who was arrested in the slaying, said homicide Sgt. Karl Robbins.
"The girl's family did not approve of the interracial relationship," Robbins said. "They were fighting about it."
"We confronted the stepdaughter, and at that point she admitted plotting the murder with her boyfriend and his cousin," Bitsis said.
Bitsis said the trio also planned to kill the girl's father, Frank Arwood, owner of a Miami produce company.
"They said they were going to take the insurance money and run off together," Bitsis said.
When Frank Arwood was notified of his wife's death, he went to Jackson High School to pick up his daughter.
"She was quite surprised. He was supposed to be dead, too," Robbins said.
Robbins said that during the night, the girl had unlocked the security bars on a window and let in the youths. One hid in a closet, and the other hid under a bed.
After Estelle Arwood went to school, Robinson found one youth and called the emergency number, Robbins said.
The names of the youths, both 15, were withheld because they were juveniles.
All three were being held yesterday on charges of first-degree murder and conspiracy.
Twice in recent years police in Dade County have taped murder victims in the moments before their deaths. In January 1985, a Miami businesswoman, shot by a robber, died clutching the phone and waiting for help. Police could not immediately find the address. There was no number on the building.
In 1980, a 13-year-old girl called to report a man breaking into her parents' home. She sounded so calm that the communications clerk was not alarmed. A car arrived in 45 minutes. She had been raped and murdered.