I didn't follow the first trial.I don't think it's nefarious that people are in multiple photos with people they don't consider friends.
What I gathered from AJ today is that at some point before/during the 1st trial when Katie/medic was asked about Caitlin Albert she said there was someone in her high school named Caitlin Albert.
AJ gathered evidence to the contrary, Brennan found out and on direct he asked K about CA and then K fessed up to a relationship but not a one-on -one friendship.
Then on cross AJ had confronted her with all the photos/events, friends in common that they had for years and even went on girls trips together.
It was AJ catching KM in a lie about CA and had he not got the evidence to prove it and Brennan finding out about it Brennan never would have asked her about CA.
IMO