SALT LAKE CITY  The man charged with the kidnapping of Elizabeth Smart, who was abducted from her home here in 2002 and held for nine months as a captive teenage wife, is back in court, and back under the microscope.

Federal prosecutors are trying to convince a judge that the defendant, Brian D. Mitchell, is not a delusional religious zealot  as a state judge concluded in 2005 when he found Mr. Mitchell mentally incompetent to stand trial  but rather a calculating criminal who simply used the trappings of religion as a tool of control and manipulation, especially in the interest of his libido.

“Lust trumped religion,” Dr. Michael Welner, a forensic psychiatrist at New York University School of Medicine, testified Friday for the United States Attorney’s Office at a mental competency hearing for Mr. Mitchell.

The hearing, which is to run through next week before Judge Dale A. Kimball of the Federal District Court here, is dissecting Mr. Mitchell’s behavior in ways, prosecutors and witnesses said, that were not possible the first time because of new information. That includes 54 interviews Dr. Welner conducted with Mr. Mitchell’s friends and relatives, additional observation of Mr. Mitchell’s behavior over the years, and deeper analysis of his religious life.