A 12-year-old boy described by a neighbor as having a volatile temper appeared in juvenile court Monday on two counts of first-degree murder in the deaths of his mother and younger brother.

The victims were found beaten and stabbed to death Sunday morning in the family's apartment outside Washington.

Police said they found a metal bar, the kind normally used to secure a car's steering wheel to prevent theft, believed to have been used in the killings.

The boy, too young to face homicide charges as an adult in Maryland, appeared at his hearing via closed-circuit television from a juvenile detention center. Judge Melanie M. Shaw Geter ordered he remain in custody until his next hearing, set for May 15. His name was not released because of his age.

The boy's mother, Katrina Denise Powe, 31, and 9-year-old brother, Mystery Toma Hillian, were found dead around 11 a.m. Sunday after Prince George's County police were called to the apartment.

Detectives interviewed the 12-year-old and arrested him there, said Cpl. Clinton Copeland. He did not know if the boy or someone else had called police.

Prosecutors said the boy's father was on his way to Maryland from North Carolina.

At 12, the defendant is believed to be one of the youngest ever charged with homicide in Maryland. If found responsible for the deaths, the boy could be held until he is 21, said Deputy State's Attorney Patricia Smoot.

"It's certainly tragic and we'll be looking at all the facts involved," Smoot said, adding, "It's incredibly unusual to have a homicide where there's someone as young as 12 involved. I'm incredibly stunned."

Neighbors said the older boy often watched his younger brother but was known in the neighborhood for having a temper.

"If he got into an argument or something, like with other kids, he would kind of explode, and like go off," Azalia Taylor told WRC-TV.

Other neighbors remembered the two boys playing football on a grass quadrangle in the center of the complex of three-story apartment buildings just inside the Capital Beltway. Balloons and a bouquet of flowers on Monday marked the building where the family lived.

"It's just devastating," said Barbara Addison, 53, a resident of the garden apartments who said her grandson played with Mystery. "He was a nice kid."