Forgive me, this is long. And a throwaway, because if my girlfriend knew how much time I spent on this she'd throw me away.
I wish we could hear the full transcript of Jay's first interview with the police. At that point I believe there's room for the narrative to go either way, and I don't think the "Lucky Jays" (credit /u/catesque) are as crazy as commonly thought around here. I'm going to tell that story with testimony and facts of the case interspersed. Like Jay said, he tells the truth but doesn't tell the truth. Hope its a friendly read.
We begin at the day of the murder. Jay has manually strangled Hae (he states the cause of death himself) in her vehicle. At that time he is in possession of Adnan's vehicle and cell phone. He moves Hae's body to the trunk of her own car. He's panicked and unsure of what to do, so he starts calling people he knows: Jenn, Patrick, Phil, and mistakenly Nisha. All of these calls ping near Woodlawn, and we accept that Hae was murdered near Woodlawn because of the narrow window of time between her being seen by Inez (or talking with Summer) and having to pick up her cousin.
One hour after Hae has been killed Jay has failed to do anything but call his friends from near the murder scene:
https://i.imgur.com/bJOjwVK.png. He leads brief conversations during the 3:00pm hour, none lasting longer than 82 seconds. At 4:12pm, after calling Jenn near Woodlawn for a second time, he drives toward Patapsco state park. He's considering burying Hae there (he describes to officers the drive and the scenery at dusk), but decides against it (in his account to police he assigns this decision to Adnan). He receives two phone calls on the cross-town trip to the Cliffs (this is around the time Jenn would have said he was "acting weird earlier in the day") that ping a cell tower near the 70/695 interchange. The drive from Woodlawn to Patapsco takes you down 695:
https://goo.gl/maps/mk2WT. The incoming 4:27pm call lasts for almost 3 minutes. At this time Jay and Jenn are having a meaningful conversation about what Jay is wrapped up in. Not necessarily that Hae is dead, but Jenn is able to infer that something is wrong.
It is now 4:30pm. Jay knows from experience that Adnan will be ready around 5:00pm. He doesn't have time to bury the body in Patapsco and pick up Adnan.
So he drives back up 695 to Adnan's car, leaves Hae in hers (he varies in saying the car was at Best Buy, at the mall where the "trunk pop" happened, and at the I-70 park n ride - I'm going with the Security Square mall for the reason below), and picks up Adnan from track practice in Adnan's car. The call placed to Adnan's voicemail at 5:15pm is Adnan checking his voicemail. He has his phone back.
They drive around (as per Adnan and Jay), smoking weed - Jay's working on his alibi, Adnan going through the motions of the day. They buy weed and go to Cathy's together. They arrive by 6:00pm, during Judge Judy. At Cathy's Adnan receives 3 phone calls:
6:07pm/6:09pm: Hae's brother - asking where Hae is/Aisha calling to tell Adnan the police will be contacting him (being of the same length and similar content the first two phone calls are basically interchangeable)
6:24pm: Detective Adcock.
That's 3 iterations in 30 minutes of the circumstances surrounding Hae's disappearance. Adnan and Jay leave Cathy's apartment to speak in Adnan's car. They discuss at length the contents of Adnan's conversations. Jay is alarmed. It's a race between him and BPD to Hae's car.
Now I'll depart from the narrative for a moment. Remember that at trial Jay testifies that Adnan dropped him off at his house after Cathy's. Jenn testifies that Jay told her the night of January 13th that Adnan dropped him off at "the mall." SK emphasizes this discrepancy. I think there's a connection between Jay's 1/13 story to Jenn - that Adnan dropped him off at the mall - and his statement to police - that Hae's car and body were at some point in the parking lot of a mall. Every "location" of Hae's body - whether it be the trunk pop(s), the park n ride, Best Buy, Edgemont street - was fabricated in late February to fit the police narrative. The only true location is the one he reveals to Jenn that night: the mall. Having to move faster than BPD can look, he asks Adnan to unwittingly bring him to the location of Hae's car and body at Security Square mall.
At around 7:00pm - 30 minutes after Adnan hangs up with Det. Adcock - Adnan and Jay arrive back at the mall. That leaves 30 minutes to have a conversation with Jay and drive the 5.5 miles to Security Square:
https://goo.gl/maps/1AIsQ. Knowing he'll need help, Jay convinces Adnan to lend him his phone again ("I never should have let someone hold my car. I never should have let someone hold my phone"). They agree to meet at the mosque at 9:00pm - 1 hour after the fast breaks. Adnan calls Yasser to tell him he'll be on his way to the mosque and gives the phone to Jay, who immediately pages Jenn (calls placed at 6:59pm and 7:00pm, respectively). Both calls ping tower L651, well within range of the parking lot. Adnan leaves, and once he's out of sight Jay gets in Hae's car. He has no time to plot and cannot risk being seen on the road. So he drives to the notorious and cadaverous Leakin park, only 4 miles away:
https://maps.google.com/maps?output=classic&dg=brw, in Hae's car, with Adnan's phone.
Google's drive time from the mall to Leakin park is 10 minutes. At 7:09 and 7:16, the "damning" Leakin park calls ring Adnan's phone. 10 minutes after Jay pages Jenn. The exact time it takes to drive from the mall to Leakin Park.
At 7:09pm Jay tells Jenn he can't talk. He's looking for a tomb. It is cold and dark and Hae's body is turning blue (remember Jay describing her lips). He drags Hae behind a log just far enough from the road, makes a bare effort to cover her body, and rushes back to the Nissan.
A perturbed Jenn calls him again at 7:16. Now the body is gone; he can talk. From Leakin park he arranges a location to be picked up by Jenn - Edmondson. A dense and criminal neighborhood that abuts Leakin Park. He hangs up and drives Hae's vehicle to its last known location - Edmondson. He spends some time deciding where and how to leave the car, decontaminating it to the best of his ability, and seeing that no one followed him. Now the car is gone. He pages Jenn from Adnan's phone, at 8:04 and 8:05. The calls ping tower L653 from the East side - Edmondson. He's ready.
Presuming Jenn was at home, she picks Jay up 7-10 minutes later at around 8:15pm. She confronts him about his behavior. He tells Jenn that Adnan killed Hae. He doesn't have time to say how, but he's involved and they need a shovel ("or was it shovels?" asks Jenn). So she drives him from Edmondson to his house, and back to Leakin Park. Its colder, darker, and he's unable to make meaningful progress. He spends "20 or 25 minutes" (his statement to police with respect to the burial time) before giving up. A cold front is coming in. Jenn goes with him to dispose of the evidence (a scene from which Adnan is suspiciously absent, if he was involved in Hae's murder), and brings Jay to Adnan's mosque to return the phone at 9:00pm. Adnan is none the wiser, thanks Jay for his promptness, and spends the next 15 minutes on the phone with Nisha and Krista, ************, as teenagers do.
Over the next few weeks the family, the press, and the police are all searching for Hae. Jenn does not understand why Jay can't tell BPD what happened. Jay says they know too much and waited too long, were at the burial site, and so on, and to never say a word or she'll catch the charge. Jenn holds up all the way to her first interrogation, when she's told she may be a suspect ("everyone's a suspect, and no one's a suspect"). This greatly distresses Jenn and she calls Jay, who asks for the details of her interaction with the police.
Jenn says the police questioned her about a number of phone calls placed from Adnan's cell phone to her home and pager on January 13th, the day of Hae's disappearance. Now I'd like to break off again, and really look at Jay's point of view after Jenn conveys this information to him.
Anyone who watches television can make their first inference about the direction of the case - they're looking at the boyfriend. And Jay remembers from his conversation with Adnan outside Cathy's on 1/13 that Hae failed to pick her cousin up by 3:15; that's how everyone knew she was missing. And Jay thinks, seeing Jenn in this frenzy, she's going to retell Jay's story about Adnan killing Hae soon. So the cops are going to have him in Adnan's car, making calls to people only he knows, at the time the police told Adnan that Hae disappeared. And if Jenn goes so far as to say that she brought him back to the burial site alone, Adnan will have an out, and Jay's completely ****ed.
So Jay instructs Jenn to tell the police enough not to get her in trouble, and send the cops his way (as per Jenn). In other words - leave out the part that leaves Adnan out of the murder. Jenn's lawyer agrees, advising Jenn not to incriminate herself, and they give Jenn's statement to the police, who have wanted Adnan ever since the anonymous phone call.
Finally Ritz and McGillivary (sp) meet Jay, the reticent accomplice. Jay says Adnan did it. The police are suspicious. Jay says Adnan said he was going to do it. The police fall in love with Jay, the unassailable witness. Murder 1, pointed directly at their favorite suspect. From there Jay and the police cooperatively cut new holes in old puzzle pieces, making them fit together.
Later Jenn will lie to provide an alibi for Jay around the suspected time of death which we know to be ******** because Adnan's phone calls Jenn's home during the time Jay is supposedly there. He's able to manipulate her into doing this 2 ways. First by telling her that she can still go to jail, and second by convincing her its OK because the "right" guy is going away.
TL;DR Jay knows from Adnan's conversations at Cathy's on 1/13/99 that Hae was suspected to have disappeared by 3:15pm. He knows Jenn will go to the cops with her story about the evidence disposal and Adnan's "involvement" because she tells him as much after her first meeting with the police. Jay sees that the cops, via Jenn, will be able to put him with Hae's killer around the time of Hae's death because he's the only one that knows and would call Jenn. He can't take himself out of the picture at that point. So he brings Adnan into it.
