Telling the Truth Falsely...
In the June 20th, 2000 Search Warrant, FBI Agent Jack Schafer referred to the expertise of Paul Ekman, Professor of Psychology at the University of California in San Francisco. Ekman authored this seminal book which trains investigators on how to tell when people are lying. He actually puts Professor Ekman and his book in the actual search warrant.
Read it for yourself here.
In the warrant, it says that on September 30th, 1996, an FBI Agent interviewed Flores' roommate, Derrick Tse. Tse told the FBI Agent that a week after Kristin vanished, Tse asked Paul Flores if he killed Kristin.
Flores responded: "Yes, I killed her and brought her to my mom's and she is still there".
Flores said it in a 'joking manner but Professor Ekman sees it differently: