A lot of times people smile in mugshots because they are high or drunk and the true reality of the crime they are being accused of hasn't hit them yet or they are proud of the crime they are being accused of. Often in Court Hearings, the Perpetrator has a remorseful and regretful look, no longer smiling. I have seen something similar, People LAUGHING in their initial interrogation interviews shortly after committing the crime, but in their court hearing looking VERY troubled.