ALLENTOWN (AP) - The homicide trial of a soldier accused of plotting with his teenage girlfriend to kill her mother a year ago has been postponed until August.

Army Spc. Caleb Barnes, 21, was scheduled for trial April 11 in Lehigh County in the stabbing death of 54-year-old Cheryl Silvonek, but the proceedings were postponed this week, The (Allentown) Morning Call reported.Court documents don't list a reason for the postponement and a judge has barred attorneys from discussing the case.Fourteen-year-old Jamie Silvonek pleaded guilty last month to first-degree murder in exchange for a sentence of 35 years to life and, according to a transcript of the proceedings, had agreed to testify against Barnes.Police say Cheryl Silvonek was stabbed in the neck March 15 as she sat with her daughter and Barnes in her sport utility vehicle in the driveway of the Silvonek family home in Upper Macungie Township.Prosecutors say the killing occurred as she talked to the couple and tried to persuade them to end their relationship.Jamie Silvonek was initially charged as a juvenile with helping Barnes clean up the crime scene and bury her mother's body. Prosecutors later charged her as an adult with homicide after investigators said they recovered deleted text messages between her and Barnes in which the teen was plotting her mother's killing."I want her gone," one message to Barnes read, according to police.Police found Cheryl Silvonek's body just before 6 a.m. in a shallow grave off a South Whitehall Township road. Her vehicle was discovered partially submerged in a pond a few miles from the Silvonek home.When police went to the family's home, they found Jamie Silvonek and Barnes naked in bed, court records say. Police say a bloody knife was found on a bench behind the home.