“He was arrested for trespassing,”
That makes no sense. People all the time go to Universities and Colleges who are not students there and do not get arrested. People all the time protest on campuses of Colleges and Universities including those who are not students or faculty and do not get arrested.
You will have to do better than that to explain why anyone was arrested for tresspassing.
I don’t think that’s the point, really. Keyes wanted to be arrested-—he even wanted to stay in jail when he was bailed out against his wishes. It was a stunt to cast light on his cause.