The thing I don't get about Jen is why would you knowingly incriminate yourself multiple times unless you genuinely believed that was what happened? Jen had no way of knowing that the police wouldn't charge her too (read the transcripts with her mum there, her mum seems to know Jack shit, and Jen just goes on and on about how she helped Jay hide all this stuff. Unless the police fed Jen the same story (that matched the forensic evidence from the car, luckily) before they spoke to Jay (again, no reason, Jen doesn't really know Adnan so why bother pointing at him).

Unless Jen was more involved than she let's on and she and Jay killed HML, or Jay killed HML and wanted help from Jen, I cant see how her police interview fits into the "it was two other random people unconnected to these two and Jay was fed information by the police that miraculously matched what he told Jen, and what she told police, prior to the police speaking to Jay."

It still doesn't make sense!