Authorities offered no further insight into the motive of a teenager accused in the shooting deaths of his father, mother and two brothers, but experts say such crimes are not unprecedented -- and they often come without any obvious warning signs. From outward appearances, Nicholas Browning was a clean-cut, success-oriented teen. 1 of 3 Nicholas W. Browning remained jailed without bond after confessing early Sunday that he killed his father, John Browning, his mother, Tamara, and his younger brothers, Gregory, 14, and Benjamin, 11, according to Baltimore County police. Browning, who turns 16 on Saturday, had no history of violence, mental health problems or drug problems, according to court documents. His father was a highly regarded business attorney, and the family lived in an affluent suburb. Browning played golf and lacrosse, was active in his church and was close to becoming an Eagle Scout. Those details were not surprising to Paul A. Mones, a defense attorney for children accused of killing their parents, who wrote a book about his work called "When a Child Kills." "This happens to kids in middle- and upper-middle-class, even upper-class homes," said Mones, who practices in Portland, Oregon. "It happens in families that, from the outside, look like normal, typical, great families." In the United States, about 300 children a year are charged with killing one or both parents, Mones said. Cases where a child kills the entire family, known as "familicide," are less frequent. Louis B. Schlesinger, a professor of a forensic psychology at John Jay College of Criminal Justice in New York, said familicide is more commonly committed by a depressed or jealous father. Slayings of relatives by teenagers "are usually spontaneous sorts of things," Schlesinger said. "With the brooding, depressive male adult, it's not spontaneous, it's much more thought through, with obsessive rumination prior to it. With a teenager, it's almost always impulsive, spontaneous, and there happens to be a loaded gun around." Mones said slayings are typically motivated by one of two factors: "extreme family dysfunction in terms of physical and emotional abuse, or severe mental health issues that pervade the family, whether it's the perpetrator or the parents or themselves. "There are cases where kids just snap out of the blue and go on a rampage, but it's really, really rare." Bill Toohey, a police spokesman, said Browning told officers where they could find the gun used in the slayings, which he tossed into some bushes near the home. The gun belonged to John Browning and was kept inside the home. Experts said easy access to guns was a common thread in cases where children kill their parents. "The biggest risk factor that was not prevented was his access to firearms, and I think that's the biggest tragedy," said Dr. Anandhi Narasimhan, a Los Angeles-based child psychiatrist. Narasimhan noted that because mental health records are confidential, it's impossible to know for sure whether Browning was suffering from mental illness or had shown other warning signs, such as bullying at school or cruelty to animals. Mones hypothesizes that such slayings are more frequent in affluent families because wealth makes abuse easier to conceal. "If you look at reports of abuse and family problems in upper-middle class families, it's really low, because the walls between the families and the world are very, very high," he said. "In lower-income communities, the police and social service agencies have a major presence, so it's nothing to call 911 when a kid's being mistreated or a neighbor hears screams."