The Difference Between Jay and Adnan's Story

Jen's story doesn't waver or change like Jay's story does her phone records prove her account and her story stays the same. Adnan did have an alibi a witness willing to come forward and tell the world that Adnan was with her during the time of the murder but Adnan's lawyers ignored her. If the state did fabricate the case against Adnan why did Jay's story change so much? The main difference in the two stories is the time between school ending and track practice 215 and 4 p.m if only Adnan had an alibi for this time right turns out he didn't.