I wanted to talk to the computer scientist but instead I talked to the fashion director.
I went to talk to the others and it made me accuse one of the family members. "You know who it is." I actually, don't. I didn't even get to question my family.
Largely trial and error. The descriptions of the various suspects are choppy and unimaginative, and there is still one particularly large error (I tried talking to the designer, and the game had me talk to the computer scientist instead.)