A man is now indicted for the kidnappings and killings of two young Tucson girls over the age of six.
Christopher Clements is accused of murdering six-year-old Isabel Celis and 13-year-old Maribel Gonzales.
The question in the minds of many; how could anyone do something like this?
KGUN 9 spoke with a UA professor about the psychology behind these types of crimes.
Note: Dr. Ole Thienhaus only spoke with KGUN about the general psychology of child predators. He never commented on the Celis or Gonzales cases, nor did he speak about Christopher Clements.
University of Arizona professor and psychiatrist Ole Thienhaus said sexual predators usually start early in life with smaller crimes.
Eventually, he adds, they progress to violent crimes.
"If you go into their background they're usually pretty pathetic failures in other areas of life," Dr. Thienhaus said.
Thienhaus said some predators choose their victims based off of age, but for others, it's a crime of opportunity.
"Some of it is determined by convenience," Thienhaus said. "In other words, what kind of kids are most easily accessible."
One thing all predators have in common, Thienhaus told us, is the need to assert power over their victims.
"The pay off is, first of all, a sense of power. It's very often stressed that it's not primarily the sexual gratification. That is sort of a fringe benefit. The sense of power and control that comes with it is absolutely critical to these people."
The professor says predators lack empathy, too.
And while there may be some occasional signs, Dr. Thienhaus said most people like this look and sound normal.
"There is no absolute safeguard. These predators are often very skilled at approaching victims at times when they are vulnerable."
Thienhaus said the most important step to keeping kids safe is knowing where they are at all times and staying reasonably cautious.
- Christopher Clements: How a convicted sex offender flew under the radar
- How the Maribel Gonzales and Isabel Celis cases were cracked
- Charges filed in the murder of Isabel Celis and Maribel Gonzales
- Isabel Celis Autopsy does not explain how she died
- Isabel Celis Timeline: From disappearance to grim discovery
- Cold Case: Maribel Gonzalez