The 15-year-old stepson of the newly appointed Charles County administrator was denied bond yesterday in La Plata after being charged with two counts of murder in the shooting deaths of his mother and 6-year-old half brother.

A day after Wednesday's shooting, which came shortly after school recessed for the day, found school officials and students at Maurice J. McDonough Senior High School wrestling with the mystery behind such a tragedy.

Charles County Sheriff's Department investigators said they believed the killings were in some way prompted by ninth grader David Richard Grzywacz's report card. Charles County public high school students received report cards Wednesday.

Grzywacz was charged as an adult with two counts of first-degree murder in the death of his mother, Heidi Bridgett, 38, and his half brother, Benjamin Lewis Bridgett, a first grader at Dr. James Craik Elementary School in nearby Pomfret. Police said Heidi Bridgett was shot in the head and chest. Benjamin was shot once in the head. Police recovered a .22 caliber rifle.

Grzywacz's stepfather, Melvin S. Bridgett, was appointed county administrator Jan. 20. Bridgett was informed of the deaths while he was attending a county commissioners' meeting in the courthouse.

Detectives said Grzywacz left school for his home about 2:15 p.m. Wednesday. At 2:45 p.m. Grzywacz called the 911 emergency police telephone number and reported the shootings.

Investigators declined yesterday to disclose the contents of the youngster's grade report, and said they did not know what his past grades were.

Grzywacz, who was described as "quiet" by a fellow student, has no known record of emotional problems, according to police.

"We have no record, and no indication at all from what family members have said that he would act in this manner," said Lt. Dave Bowling of the homicide unit.

McDonough Principal Herman L. Murrell called his 76-member teaching staff together before school began yesterday morning and ordered them not to speak with the media. He also asked them not to discuss the shooting with students. But one teacher, who asked not to be identified, described Grzywacz as "innocent and naive."

"We were told not to talk about it today, but the kids had to," the teacher said. "They just had to talk about it a little anyway."

Standing in a wet snow in the school's parking lot after the last class, the teacher added, "The kids couldn't handle it today. I couldn't handle it," her eyes beginning to water. "I almost didn't make it through seventh period."

Murrell said the shooting has had a "devastating" impact on the teaching staff and the 1,330-member student body and that counseling was made available to those who need it.

"We are doing everything possible to assist these students and teachers who are experiencing stress related to this," Murrell said. He acknowledged that some high school students are easily influenced and expressed concern that there not be a "copycat" incident.

Michelle Sowell, a 16-year-old high school junior who said Grzywacz once lived down the street from her, said she didn't know him well but that "he was really quiet."

Grzywacz, a short, slight freshman, tried out for the school's junior varsity football team last fall but was cut after the first week "because he was too small," said one instructor who also asked not to be identified. The instructor said that the team's coach phoned Grzywacz's mother and that they both "agreed that it was in his best interest" not to play on the team.

During yesterday's bond hearing before District Judge Robert C. Nalley, Grzywacz sat in the first row, his deep-set eyes staring straight ahead. His black, neatly trimmed hair was tucked into the collar of his prison overalls as he nervously gritted his teeth and tapped his feet. Charles County State's Attorney Richard Cooper requested that bond be denied, saying, "I don't know where he {Grzywacz} would go."

Grzywacz was taken last night to a juvenile detention facility outside the county.

His father, Thomas Grzywacz, attended the bond hearing but would not comment.

A spokesman for Charles County, where Bridgett has been an employee for a dozen years, issued a statement calling it a "tragedy for the community."