LEADS throughout to ADD background about the murders and the case; No pickup.

 HUNTSVILLE, Texas

A state appeals court on Tuesday halted the execution of a triple   murderer after attorneys argued jurors should have been allowed to consider   his troubled childhood during his sentencing.

<That was the only issue I raised,> said defense lawyer Randy Schaffer. <I   asked the court to stay the execution and permit me to argue the case when   it reconvenes in September.>  Mark Robertson, 35, whose lengthy criminal history started before he was a teenager, was set to die by lethal injection Wednesday for the execution-style slaying of Edna Brau, the grandmother of one of his friends, at her home in Dallas.

   Robertson received a life sentence for fatally shooting Brau's grandson, Sean Hill, 19, and another life term for killing a convenience store clerk in Dallas 10 days earlier.

Authorities said that after the shootings, Robertson took money from Brau's purse and drove off in her blue Cadillac.

He was arrested eight days later when police spotted the car in the parking lot of a Las Vegas casino.

Tuesday's ruling by the Texas Court of Criminal Appeals means the court will hear Robertson's appeal again. At that time, it can either send the case back for a new trial, order a new resentencing or reject the appeal.

Officials at the Dallas County District Attorney's Office did not immediately return a phone call seeking comment.

Robertson's 1991 trial came during a two-year period before the Texas legislature clarified guidelines regarding jury instructions in the wake of a U.S. Supreme Court ruling in another Texas case that involved a mentally retarded death row inmate.

Lawyers in that case challenged the conviction, saying jurors should have been allowed to consider the defendant's mental retardation as a <special circumstance> when they considered punishment.

Robertson's attorneys similarly argued that growing up with an alcoholic father, being abused as a child and Robertson's ensuing drug abuse also should have been considered by a jury as mitigating evidence.

If a jury finds such evidence, a life sentence is imposed.

Tuesday's ruling by the Texas Court of Criminal Appeals is the latest in a series of twists in Robertson's case.

In January 2002, the 5th U.S. Circuit Court of Appeals, acting on an order from the Supreme Court, threw out Robertson's death sentence, then reinstated it earlier this year after a rehearing requested by Texas officials.

Last Friday, the Supreme Court refused to overturn the appeals court decision, which is when Schaffer brought the case back to the state court that halted the execution Tuesday.

Twenty inmates have been executed this year in Texas, which has the United States' highest execution rate. Two more are scheduled for September.