SAN DIEGO — David Westerfield broke down and cried at the defense table Thursday afternoon as his younger sister tried to convince jurors not to execute him for the murder of Danielle van Dam.

The convicted killer has worn a poker face for much of the trial, showing no hint of emotion last week when the jury found him guilty, and wearing a bland expression Wednesday when her grief-stricken parents described their loss. But when his sister took the stand in his defense, Westerfield turned a deep pink, his mouth quivered and he wiped tears from his reddened eyes.

"Do you love your brother?" defense lawyer Steven Feldman asked the 46-year-old mother, identified in court only as Tania P. for privacy reasons.

"Yes, I do," she replied.

Jurors could begin deliberating Westerfield's fate as early as next Wednesday. The six men and six women on the panel must sentence him to life in prison without parole or to death for Danielle's February killing. The jury must decide whether factors aggravating his guilt, such as the heinousness of Danielle's murder, the devastation it caused her family and a previous incident in which Westerfield may have inappropriately touched a young girl, outweigh circumstances that lessen his guilt, such as good he did before the murder.

Prosecutors have acknowledged that it is difficult to comprehend how Westerfield, a successful engineer with two children and a nice house in an upscale suburb, secretly hid a life as a pedophile who steadily worked his way from collecting violent child pornography to murdering his 7-year-old neighbor.

And Tania's recounting of Westerfield's life — the most intimate glimpse yet offered the jury — was also devoid of explanation for his descent. A tall, pale woman with bottle blonde shoulder-length hair and thick bangs, Tania portrayed Westerfield's upbringing as idyllic and said that, as an adult, he was a devoted father who loved traditional home life.

Westerfield, whom she called by his middle name, Alan, was the eldest of two boys and a girl. Until Westerfield was a high school junior, the family lived in Maine, where her father was a member of the state legislature. She described summers of water skiing and swimming at an island cottage and winters of ice skating and skiing. Westerfield, she said, held jobs as a lifeguard and blueberry picker and the family lived in a big farm house owned by her great-grandmother.

"We had a very nice childhood in my opinion," said Tania, smiling across the courtroom at Westerfield. He returned the grin.

She said her family eventually moved to San Diego and her parents decided to divorce. Her brother, she said, expressed dismay that the children he would someday have would not have a grandparents' home to go to at holidays.

"He wanted like the traditional family life," she said.

In the last row of the courtroom, Danielle's mother, Brenda van Dam, listened closely, at times craning her neck to see the witness stand.

Westerfield's mother, Laura, sat next to her husband in the gallery dabbing at her eyes with a tissue.

Tania said that when her father died in 1993, just three years after her other brother, Earl, had succumbed to a terminal illness, it was Westerfield who stepped forward to care for the family.

"He was depressed, but he took care of everything, the arrangements, the hospital, very sensitive to everyone's needs," she said.

She said he and his former wife, Jackie, often threw parties for the entire family and that Westerfield was a very involved father to his two children, Neal and Lisa. She recalled him teaching them how to care for the birds in an aviary he built and attending their school functions. When Jackie divorced him in 1996, she said, his primary concern was the effect on the children.

"He wanted them to grow up in a two-parent home," she said.

In a brief cross-examination, prosecutor Jeff Dusek juxtaposed Westerfield's close relationship with his children with the van Dam's grief.

"He got to see all the milestones in her life," he asked, referring to Westerfield's daughter.

"Yes," said Tania.

"He was able to enjoy the growth of his children?" Dusek asked.

As Tania replied "Yes," Brenda van Dam, her face scarlet and wet with tears, rushed from court with a loud sob.

Westerfield's aunt, Jean, also took the stand, testifying that he volunteered to help her care for his grandmother, who was stricken with Alzheimer's.

Another defense witness, Marie Gunther, the mother of a classmate of Neal Westerfield, said that, throughout Neal's school years, his father was a constant presence at school plays, band concerts and soccer games.

"I just saw David and Neal all the time together. They were very close," she said.

Pressed by Dusek, though, she called herself only a "social acquaintance."

"I don't know anything about his personal life," she said.

Jurors also heard from Westerfield's ex-girlfriend, identified as Susan L., and her daughter, Christina Gonzales. Both women said Westerfield was generous with his money and his home. When she testified during the trial, Gonzales said he took her in when she was in an abusive relationship and bought her food and diapers.

Susan L. said Westerfield paid her bills when she was on disability and even hired a housekeeper for her. He also helped her buy an SUV, she said.

But prosecutor Dusek pointed out that Susan left Westerfield on three different occasions and suggested that the money he gave her hardly translated to good character.

"He made a lot of money," he said.

"Yes," she acknowledged.

"He like to spend it on you," he asked.

"Yes," she said.