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.
Brice McMillan told deputies the boy was released the following morning, but was tied up again that night for bad behavior, according to the AP.
According to arrest warrants for the couple, the boy sustained "bruising to the wrist, cuts to entire body, missing flesh from buttocks, results from being tied to a tree for approximately 18 hours, resulting in death."
He was found unresponsive by his stepmother Thursday afternoon. She began CPR and alerted the police, but the teenager was pronounced dead on arrival after he was taken to the hospital.
"There are people who abuse their children in a frenzy of rage," said James Garbarino, forensic psychologist at Loyola University and author of "Children and the Dark Side of Human Experience."
"People do stuff beyond what is characteristic for them. There is a burst of intensity, frustration and anger. They simply lose control," he said.
Welner said parents can sometimes become overwhelmed by their own inability to manage a situation.
"People who manage their anger are not a danger to children," he said. "People who cannot and become overwhelmed are a danger.
"Abusive parents believe they are disciplining their children," he said. "They become increasingly angry with a child for not responding to discipline. Discipline becomes increasingly destructive as the parent comes to interpret the lack of responsiveness by the child as acting out against them."
On Friday, the mother of a 5-year-old Los Angeles boy was arrested by police who found countless cigarette burns all over the child's body, including his genitals. The boy was unable to open his hands because he had been forced to put them flat on a hot stove, and was repeatedly beaten and forced to sit in his own urine, according to Los Angeles police.
"In my time in policing in 27 years, I have never seen anybody with these kinds of injuries that has lived," L.A. police department First Assistant Chief James McDonnell said. "And this kid must have a tremendous will to live to be able to still hang on, despite what he's been through."
The boy's mother, Starkeisha Brown, 24, was arrested after she turned herself in to police on Friday evening.
Krystal Matthews, 19, who police described as Brown's live-in girlfriend, was arrested earlier Friday when she showed up for an appointment at the state Department of Children's Services with another child she claimed was the boy, police said.
The boy was hospitalized in critical condition, officials said over the weekend.
The experts consulted by ABC News.com called this long-term abuse "premeditated."
"There are people whose thinking and feeling becomes so distorted it is as if they live on another planet or dimension," Garbarino said. "If you ask them about their reason for abuse, they can give, what seems to them, rational coherent narrative. The account seems totally bizarre to you, but to them it seems like a coherent story."
According to Welner, "Rather than seeing a child as vulnerable and immature, the parent sees the child's lack of response to discipline as a source of his own failure. This behavior is premeditated and reflects increasing vindictiveness."
The extreme nature of these cases makes them stand out, but according to federal statistics, nearly 1 million children are abused in the United States every day.
According to a Health and Human Services Department report, four children die every day as a result of abuse or neglect, and three-quarters of the victims are less than 4 years old.
ABCNews.com's Dean Schabner contributed to this report.