Rachel O'Donnell last saw her daughter, Sabina Rose, in May 2010, when Sabina took her to lunch for Mother's Day. A few weeks later, Sabina O'Donnell was dead. Her clothes, makeup, camera, jewelry, and an uncashed paycheck were left strewed across a trash-filled vacant lot on the edge of Northern Liberties, along with her blood.

Later, at the medical examiner's office, Rachel O'Donnell was advised against seeing her daughter one last time. Sabina, just shy of her 21st birthday, had been raped, badly beaten, and strangled, her bra knotted so tightly around her neck that the underwire was embedded in her skin.

"They didn't think I should actually see her body, so they had me identify her from a photograph," Rachel O'Donnell said in a shaky voice, tears falling.

O'Donnell's mother was the sole witness called Tuesday, the first day of accused killer Donte Johnson's murder trial in Common Pleas Court. Lawyers expect testimony to last about five days.

Johnson, a 20-year-old North Philadelphia man who has been imprisoned since about two weeks after O'Donnell's death in June 2010, has turned down at least two attempts at negotiating a plea agreement. He faces life in prison.

In his opening statements, Johnson's attorney, Lee Mandell, cautioned jurors not to rush to judgment, saying O'Donnell's death was not a case of first-degree murder. He also asked jurors not to let sympathy for O'Donnell's relatives, who sat in court on Tuesday and wept at times, interfere with their decision-making.

"No one disagrees that this was a horrible crime," he said.

Assistant District Attorney Richard Sax described O'Donnell as gentle and "full of life." She spent her last hours watching a movie and eating popcorn at a friend's house before getting on a bike and pedaling a few blocks to where she lived with her stepfather at Fourth Street and Girard Avenue, he said.

Johnson, then 18, was biking around the neighborhood and briefly followed another woman on a bike, Sax said. But that woman never strayed from brightly lit streets, and she was larger than the 5-foot-3, 100-pound O'Donnell, whom Johnson spotted around 3 a.m. as she headed toward home.

"She was perfect for exactly what he was looking for, as she pedaled into that dark, foreboding lot that was to be her personal hell," Sax said.

After Johnson dragged O'Donnell behind her own apartment building, Sax said, he raped her violently, beat her, and smashed her head against a rock. Holding aloft a bloodstained undershirt left at the scene after the killing, Sax said that to convict Johnson, the jury need only consider the evidence: Investigators collected numerous DNA samples from O'Donnell's body, Johnson was captured on surveillance cameras in the area, and he also confessed to police.

Mandell outlined several areas where jurors might find "reasonable doubt" in the case. The people who analyze DNA can make mistakes, he said.

Johnson's mental state is also expected to be a big factor in his defense. Mandell said that a series of psychological tests performed on Johnson found that he suffers from a level of mental impairment that would have prevented him from giving the police a "knowledgeable, truthful" confession about O'Donnell's death.

"As he sits over there today, he's an innocent man," he said. "That's the law."

Testimony is expected to continue Wednesday.

Contact Allison Steele at 215-854-2641 or asteele@phillynews.com. Follow on Twitter @AESteele.