When Timothy Scott Sherman shot and killed his mother and adoptive father while they slept, the case disturbed the normally quiet life in the small Harford County hamlet of Hickory.
A quarter-century later, another family murder has rocked the county, in neighboring Bel Air. In that case, Robert C. Richardson III has confessed to killing his father, according to authorities.
The state's attorney for Harford County, Joseph I. Cassilly, a gruff no-nonsense lawman, prosecuted the 1987 Sherman case in the beginning of his career and now takes the lead on the Richardson case, which has once again cast a pall over his community.
Both cases not only shocked area residents but have raised many questions, some unanswerable. Sherman and Richardson were both teenagers who went to C. Milton Wright High School and were living in middle-class neighborhoods with their families at the time of the killings.
But while much has been learned about Sherman, who confessed a decade after the crime, the search for answers in the Richardson case has just begun.
No one knows for sure what caused Richardson to allegedly shoot his father, according to investigators who say they are trying to understand his motive. And no one knows for sure what went on in their home. Neighbors say they heard angry shouts from inside for years, though no records or reports of domestic abuse have been made public.
Moreover, it's difficult to understand why.
"I don't know that it's easy to draw a conclusion or comparison from one to the next," Cassilly said of the two cases.
Cases of patricide or matricide are rare — roughly 250 parents are killed each year by their children, or less than 2 percent of all murders in 2010. By comparison, an average of 55 people are struck by lightning a year in the country.
But the subject has been widely studied by academics and forensic psychologists and psychiatrists.
Harold J. Bursztajn, co-founder of the Program in Psychiatry and the Law at Harvard Medical School, said the fundamental question in any case of patricide or matricide is: "Did this happen because the defendant was bad or did this happen because the defendant was mad? And there is a whole spectrum in between."
Children who kill their parents typically do so for one of three reasons, said David M. Reiss, a California-based psychiatrist with 25 years of experience in the field. The children are either psychotic, anti-social, or the victim of severe abuse that is "repetitive to the point that the kid loses track of right or wrong," Reiss said.
Experts say that abuse — physical, sexual or verbal, especially by constant humiliation — is the most common reason for patricide or the less common matricide.
Kathleen M. Heide, a professor of criminology at the University of South Florida, Tampa, and the author of "Why Kids Kill Parents: Child Abuse and Adolescent Homicide," said the most common reason a child kills a parent is because of severe abuse. "That usually can be documented," she said.
The children sometimes have a history of running away, she added. "Typically they killed because they are desperate or they are terrified," she said.
In the past 30 years, Maryland has seen at least five high-profile cases, in addition to Richardson's.
In 2008, Nicholas W. Browning, then 15, killed his parents and two younger brothers as they slept in their Cockeysville home. Browning was sentenced to four life terms.
Lewin Carlton Powell III used a bat to bludgeon his mother to death in their Towson home in 2008 when he was 16. He was sentenced to life in prison.
Michael Edward Joseph Reiriz pleaded guilty to killing his grandparents with a Louisville Slugger in their Guilford bedroom in 1994. He was 31 at the time and received two life sentences.