Welner said that people who work in the sex industry often struggle to fit in to their communities. "Often they long for a day when they will have a legitimate life," he said.
It is still too early to tell which of the possible explanations best describes what happened to Birgfeld. And Dvoskin warned that there are significant differences between behavior like having an affair with a student, which can be motivated by a lack of impulse control, and running an escort service, which requires much more planning.
Until more is known, Birgfeld's friends and family will probably continue to be surprised by how little they know about the young woman they thought they knew.
Forensic psychologist Martin Williams wondered, "You have to ask, is the escort service the exception or is the family life the exception?"
ABC News Consultant Dr. Michael Welner is chairman of The Forensic Panel, a national forensic science practice. He is developing an evidence-based test called the Depravity Scale, http://depravityscale.org, which invites Americans to participate in surveys that are used to form a legal standard of what represents worst crimes.