The sister of convicted killer Derrick Todd Lee (search) reminisced about their childhood baseball games and bird-hunting trips together as she pleaded for her brother's life during the penalty phase of Lee's murder trial Wednesday.

Lee, convicted of beating and stabbing to death 22-year-old Charlotte Murray Pace (search) in 2002, has received a life sentence in a second slaying and is accused of killing five other women.

His sister Tarshia Fontenot (search) apologized to the victims' families from the witness stand. "I am just so sorry for your loss. I'm sorry, my family's sorry for your loss," she said, crying.

Lee cried as Fontenot talked about their childhood. He showed no emotion when his verdict was read Tuesday or during testimony from Pace's family earlier in the penalty phase.

On cross-examination, Fontenot acknowledged she filed a police complaint in 1989, saying her brother threatened to hit her after breaking into his mother's home and that "no one could stop him."

Most of the jurors were in tears as they looked at pictures of Pace as a child and listened to her mother, father and sister describe their grief.

"There's no peace in sleep. There's no joy in holidays. ... It's changed the world. It's harder, darker, a more frightening place than I ever thought it could be," Pace's mother, Ann, testified.

It took the jury just 80 minutes to find Lee guilty of first-degree murder. The same jury must now vote unanimously for the death penalty or give Lee a life sentence.

Lee was sentenced to life in August after being convicted of second-degree murder in the death of 21-year-old Geralyn DeSoto. Authorities say they have linked Lee through DNA evidence to the deaths of seven women from 1998 to 2003.

Defense attorneys argued Wednesday that Lee should be spared the death penalty because he is retarded and the U.S. Supreme Court ruled in 2002 that the mentally retarded cannot be executed.

A former school official from Lee's hometown testified that Lee had been a special education student. Lee's lawyer, Bruce Unangst, also showed jurors the results of two tests administered by a neuropsychologist that indicate Lee is mentally retarded.

The prosecution has rejected the defense's mental retardation claims, saying their own psychologist and psychiatrist examined Lee and found him not to be retarded.

Louisiana law lets a jury determine mental retardation after reaching a verdict, unless defense attorneys and prosecutors agree beforehand to let a judge decide.