Lorraine and John first become involved with Mr. Pignati when they are prank calling people. Lorraine is supposed to choose a phone number randomly from the phone book, but she chooses a number based on a neighborhood address. While speaking to Mr. Pignati, she realizes how lonely Mr. Pignati is. Unfortunately, Mr. Pignati is not only lonely but trusting, so he is more than willing to donate to their fraudulent "L & J Fund." Lorraine and John make arrangements to pick up their ten dollar donation the following day.

When John and Lorraine go to his house the next day, Lorraine has second thoughts about pranking Mr. Pignati. She realizes that he lives alone in an untidy home, and she is also fearful about what he could do to them. While visiting him, Mr. Pignati shows them his collection of pig figurines and invites them to go with him to the zoo the following day. 

The relationship between Mr. Pignati, John, and Lorraine develops because of their collective loneliness and isolation. By confiding in one another, they develop a support system that all of them lack. Their relationship is ultimately destroyed by John and Lorraine's betrayal of Mr. Pignati's trust because they not only throw a party in his home, but disrespect his private belongings that symbolize his life with his deceased wife. 

Lorraine and John get involved with Mr. Pignati (the Pigman) through a random telephone prank.  They choose him to follow because they are social outcasts themselves and do not have the best intentions for befriending Mr. Pignati.  Basically, they want to take advantage of him by chronicling their interactions.  They feel this gives them an advantage.  The story was written in 1968, so it is a version of cyber-bullying. 

Going beyond the surface, the two become involved with him for several reasons.  It allows John and Lorraine to form a bond through a shared secret oath.  This gives them sense of belonging and fills, in part, the loneliness of being outcast.  Mr. Pignati, being random, is another key aspect of the story because it hints the two teens are not quite as rebellious as one might imagine.  It would be easier to pick a student from school for example, but by picking a random person they decrease the risk of an authority figure catching them.  This indicates they are exited by the rebelliousness of the action, but still scared of the consequences. 

Why are Lorraine and John writing The Pigman?

The book's opening "oath" tells readers a bit about the answer to this question:

Being of sound mind and body on this 15th day of April in our sophomore year at Franklin High School, let it be known that Lorraine Jensen and John Conlan have decided to record the facts, and only the facts about our experiences with Mr. Angelo Pignati.

John and Lorraine finish the book's opening oath by telling readers that nothing but the truth is being recorded in the following pages. We have no idea who John, Lorraine, or Mr. Pignati is at this point, but the first two chapters of the book then inform readers that John and Lorraine are writing the book's very pages for two general reasons. First, the book is somewhat of a tribute to Mr. Pignati and the relationship that the two protagonists established with him. The second reason for writing the book is that the writing process is essentially a coping mechanism to help John and Lorraine deal with their feelings about Mr. Pignati, their experiences with him, and his death. Lorraine's first chapter (chapter 2) flat out tells readers that she and John feel compelled to write down the events of the last few months. They want to write them down while the details are fresh and before they decide to repress all of those emotions.

It’s just that some very strange things have happened to us during the last few months, and we feel we should write them down while they’re fresh in our minds. It’s got to be written now before John and I mature and repress the whole thing.

Why are Lorraine and John writing The Pigman?

John and Lorraine are telling the story of the Pigman, Mr. Pignati, whom they met and grew to care about. The story is told by both of them, so that you get two perspectives on the events. In some ways, they are trying to make sense of the relationship they had with the Pigman, and his death.