As heartbreaking as they are horrific, three cases of extremely violent torture of children have made headlines in recent days, leaving observers to wonder how anyone could be so cruel.
In two of the cases, the children died. In one, a man stomped and kicked a toddler, believed to be his son, in front of witnesses, and in the other, a 13-year-old boy was tied to a tree for two nights.
In the third case, Los Angeles police characterized the lengthy torture of a 5-year-old boy as one of the worst cases of child abuse they had ever seen. He was burned with cigarette butts all over his body, including his genitals, and forced to place his hands on a hot stove.
Forensic experts consulted by ABC News.com said the cases represent a spectrum of psychological reasons for why adults abuse children, from sheer psychosis to frenzied rage.
"Sometimes, profound child abuse reflects the psychological illness of a parent, but more often it reflects a parent who has become overwhelmed by his inability to manage a situation," said Dr. Michael Welner, a forensic psychiatrist and ABC News consultant.
On Sunday, an officer shot and killed Sergio Casian Aguilar, 27, who stomped and kicked a 2-year-old -- who police believe was his son -- to death on a dark country road in Turlock, Calif.
Before the police arrived, witnesses say they tried to stop Aguilar from brutally beating and repeatedly throwing the child to the ground, according to authorities.
Due to the boy's severe injuries, police await further DNA testing to accurately determine his age and identity, said deputy Royjindar Singh of the Stanislaus County Sheriff's Department.
Drivers stopped and tried to intervene when they saw Aguilar on the side of the road, next to his pickup truck, beating the child.
"Witnesses said he shook, stomped, kicked and slapped the baby. They tried to intervene, but were unable to stop him," Singh said.
Police arrived on the scene by helicopter, and when Aguilar refused the officers' orders to stop beating the child, they shot him dead.
One witness, Dan Robinson, a volunteer fire chief who arrived at the scene and tried to stop Aguilar, told the Associated Press that Aguilar said he believed the boy was possessed by "demons."
Belief that a child is possessed is a common reason for extreme abuse by psychotic individuals, said Welner, who testified in the Andrea Yates case.
Yates, who drowned her five children in 2001, was found not guilty by reason of insanity, because she said she believed her children were demonically possessed.
"A person who believes their child is possessed does not believe they're torturing that child. They don't believe it is abuse," said Welner, who is developing an evidence-based test called the Depravity Scale, which standardizes distinctions between the worst crimes.
"If the man in this case believed the boy was possessed, then he believed he was destroying the devil. He ceased to relate to the child as a living person and saw it, instead, as a dangerous entity," he said.
On Monday, Brice Brian McMillan, 41, and his wife, 36-year-old Sandra Elizabeth McMillan of Macclesfield, N.C., appeared in a North Carolina court to face charges of murder and felony child abuse.
The couple did not enter a plea, but police allege the couple tied their 13-year-old son to a tree on the night of June 10 and forced him to sleep outside.