PITTSBURGH — An 11-year-old boy apparently covered his shotgun with a blanket to keep it hidden when he left his bedroom, went downstairs and fatally shot his father's pregnant girlfriend in the head as she slept, a prosecutor said Monday.

The blue blanket, which has a quarter-sized hole that appeared to be singed from a shotgun blast, supports a claim that the crime was premeditated, Lawrence County District Attorney John Bongivengo said.

Police found the blanket in the farmhouse where the boy, Jordan Brown, lived with his father; the father's girlfriend, Kenzie Marie Houk; and her two daughters, ages 7 and 4. Houk was killed Friday morning while Brown's father was at work and the two girls were in the home, authorities believe.

"The operating theory is that he covered the gun with the blanket to hide it when he came downstairs" from his bedroom to shoot Houk, who was in a first-floor bedroom, Bongivengo said. "It wasn't used to muffle (the shot) or anything, the blanket wasn't thick enough for that."

Brown got the youth-sized shotgun as a Christmas present and used it to win a turkey shoot on Valentine's Day.

After shooting Houk, the boy ran to get on a school bus with the 7-year-old, who saw him toss something from his pocket on the ground, Bongivengo said. Police later found a spent 20-gauge shotgun shell at that spot.

The girl later implicated the boy in the killing, saying she saw him with what she believed to be a shotgun and heard a loud bang, Bongivengo said.

Brown is charged as an adult with criminal homicide. In Pennsylvania, there is no criminal homicide charge in juvenile court.

"Because the juvenile system only has jurisdiction until he's 21, the last thing I want is a 21-year-old who's going to be out on the streets and willing to kill you," Bongivengo said.

Houk's family told police the boy had threatened her and her 7-year-old daughter in the weeks before the shooting, Bongivengo said. Houk's family said the boy might have been jealous of Houk and her children.

"If this person were 18, we'd be looking at pursuing the death penalty," Bongivengo said.

Defense attorney Dennis Elisco said he plans to ask a judge to move the case to juvenile court and to have the boy released on bail to his father. Brown is being held at the Lawrence County Jail, where jail officials said they don't have adequate accommodations for someone that young. He is being kept separate from the jail's approximately 300 adult inmates.