A judge in October found 24-year-old Brian Rockwell Williams mentally incompetent to stand trial, and he was sent to a state mental hospital for treatment. Once his competency was restored, he was returned to San Diego, where murder charges were re-instated. The defendant faces 52 years to life in prison if convicted.Williams is charged in the July 18 deaths of Donna Williams, a veteran San Diego police child-abuse detective, and Briana Williams, a Mount Carmel High School graduate who had planned to attend a San Francisco design college.On Tuesday in court, Williams pleaded not guilty to a pair of murder charges. A status conference was set for July 30.At Williams' arraignment last summer, defense attorney Richard Gates told reporters that the defendant had been diagnosed with schizophrenia but was not undergoing treatment at the time of the murders.In late June of last year, officers went to the Williams family home on a call of a disturbance involving the son, according to police.About 1:15 a.m. July 18, residents were awakened by the sounds of a woman screaming. They looked outside to see Briana Williams struggling with her 6-foot, 300-pound brother on the balcony of their home on Paseo Montril, outside her bedroom window, prosecutor Kristen Spieler said.At one point, Briana was seen hanging from the balcony by her hands, and eventually dropped to the pavement below, according to Spieler, who said the defendant was seen calmly walking back into the home.Within minutes, police arrived and found the defendant in the front yard, standing a few feet from where his sister lay dying, the prosecutor said. Near her body was a bloody knife, Spieler said.When officers made entry into the home, they found the body of Donna Williams face-down in Briana's bedroom, the prosecutor said.