In actuality, only the following details are consistent throughout all of Jay's stories: (1) Adnan killed Hae on January 13, 1999, at 3:40 p.m.; (2) Jay was at Jenn's house until 3:40 p.m.; (3) Hae's car was first dumped at the Park 'n'Ride; (4) Adnan went to track practice that day; and (5) she was subsequently sighted at the park with Adnan. The rest is detail and variation.
Jay tells these stories in the first person. He claims to know everything about the case, including information about events and people involved beyond what was already known at the time they were told. For example, he claims to know that Hae was seen leaving Jenn's house late on January 12th with a young man who wasn't identified by name but who many readers assumed to be Jenn's ex-boyfriend Tyler, based on descriptions provided by Jay of both individuals.
Jay also tells some stories in which he plays a role. For example, he tells one story in which he claims that he saw Adnan after the murder and that Adnan confessed to him. There are other stories in which he claims that he knew certain facts about the case when they occurred that other people didn't know yet, such as the fact that Hae's body had not been found at the time he told them. In most cases, however, he simply makes up the details as he goes along. He never mentions any conversations he had with other people or any documents that may have helped him shape his stories.
Why is Jay's narrative so crucial to the investigation? Jay was a critical witness who provided information that might show Adnan murdered Hae. Adnan is still in jail because of him. Do you believe the cop's line of inquiry is reasonable? Is he asking you leading questions? What does his tone of voice suggest?
Now, let's look at some specific questions that Detective Griffin asks Jay during their interview. They are simple questions designed to get Jay to tell his story again in his own words. Notice how each question provides more detail about what happened on the night of May 11, 1999. This helps bring out the truth in what he says.
Question: "Did you know her well?"
Jay's response: "No."
Griffin: "She didn't go to your school?"
Griffin: "You don't hang around with anyone at school that would want to harm her?"
Griffin: "Do you have any idea who could've done this to her?"
Why would he alter this aspect of his story? To blame Adnan while also defending himself He makes it appear like Adnan planned the murder, but when it appears that Jay would be prosecuted for failing to notify the police or warn Hae, he makes it appear that he didn't take it seriously until it was too late. This changes our perception of him from a lonely kid who is obsessed with crime fiction to a person who is aware of his responsibility and tries to fulfill it as best he can.
Also, altering his story could help him avoid punishment. If prosecutors believe that he has something to hide, they may try to force him to change his story. For example, if he admits to hitting Hae but claims not to have known she was dead, this might not result in prosecution since no crime was committed within the state of Maryland. However, if he denies hitting her at all, this could lead to charges being filed against him.
Finally, altering your story is a common technique used by witnesses who want to protect themselves. Since we know from experience that people don't usually get punished for witnessing crimes, people tend to think there must be something else you can do besides witness a crime - like attacking someone- and so they try to explain away their failure to help Hae earlier by saying that they didn't think they could have done anything. But even if they couldn't have saved her, there's still no reason for them to lie about what they saw.