The Case Against Adnan Syed is revisiting the biggest true crime mystery of this decade.

On December 10, 2014, the very first episode of Serial dropped on the podcast charts.

Within days of the podcast dropping, millions of people became obsessed with the murder of Baltimore high school student Hae Min Lee, and the trial and conviction of her ex-boyfriend, Adnan Syed.

As Serial host Sarah Koenig spoke to Adnan from behind bars, and retraced his steps on the day Hae was murdered, we became more and more desperate for answers.

Did Adnan actually do it?

Watch the full trailer for The Case Against Adnan Syed here. Post continues below…

How could his lawyer get away with being so incompetent?

What was his so-called friend Jay Wilds hiding?

Was the cell tower evidence inaccurate?

What about the location of Hae’s car?

Thousands of thought pieces were penned, countless Serial spin-off podcasts were launched, millions of group chats were buzzing with opinions on the case.

Then, after 12 intense episodes, Sarah wrapped up her investigation into Hae and Adnan and moved on to her next story.

Now, almost five years later, a four-part documentary is diving back into the case.

Here’s everything we’ve learned so far:

1.We learned more about Adnan and Hae’s relationship.

In the first episode, we learn that Hae was from a strict family and she wasn’t allowed to have a boyfriend. Despite this, she called Adnan her “baby” and wrote about how he was the “sweetest guy”.

The young couple would park in supermarket car parks to make out. They would tell their parents they were staying the night at their friends’ houses, so they could sneak off to a hotel.

When Adnan was crowned Prom Prince, they danced to K-Ci and JoJo’s All My Life. “How could I not fall in love with this guy,” Hae wrote in her diary.

"I remember our first kiss was at the prom," Adnan says over the phone from prison. "That was one of the happiest moments of my life."

2. We discovered more about Don, Hae's boyfriend at the time of her murder.

In episode one we learn that Don Clinedinst, Hae's older boyfriend, was acting suspicious around the time of her disappearance.

Someone who worked with Don at LensCrafters, said the then 22-year-old had scratch marks and bandages on his forearms when he was telling them about Hae's disappearance.

Don said the injuries occurred while he was working on his car, and detectives didn't question him about Hae's disappearance until three weeks later.

3. We saw the crime scene and Hae's body.

In the most haunting scene in the documentary, we were shown a crime scene photo of Hae's body in Leakin Park.

Although this moment was very confronting, it was used by the documentarians to prove that Hae was probably buried way later than 7:30pm like the prosecution claimed.

Hae's body showed signs of lividity, the postmortem pooling of blood inside a corpse, surrounding a diamond shaped mark on her shoulder. According to the pathologist in the documentary, that mark could only occur from Hae lying face down on an object with that shape for at least eight to 12 hours.

They concluded that Hae's body wasn't buried until between 10:30pm and 2:30pm that night.

There were also no signs of a struggle on Hae's body, meaning the murder probably didn't happen in the close confines of her car.

4. We learned that Hae's car was likely moved way after her death.

In the second episode, investigators travel to the spot where Hae's car was found in February 2000, at least six weeks after her death.

Local long time residents tell the investigators there's no way a car would've have stayed in that spot for over six weeks without being vandalised or towed away.

A scientist also pointed out that there were blades of grass on the car's wheels - and given the weather at the time - it's likely the car was only there for a week at most.

5. We discovered Jay and Adnan weren't that close.

Despite Jay claiming he helped Adnan bury Hae's body in Leakin Park, the pair weren't actually that close.

According to their mutual friends, Jay and Adnan would only hang out occasionally. Jay spent most of his time with his girlfriend, Stephanie McPherson, and his best friend, Jennifer Pusateri.

"Me and Jay would have met when we were in middle school. We used to ride bikes together. We would smoke weed together," Adnan explains over the phone in the documentary.

"But then for a period of time we may not see each other. So that was my relationship with him throughout most of high school," he continued.

"Me and Stephanie were always really close and then Stephanie started dating Jay. That's really how I stayed in touch with Jay."

"I know Jay," explained Laura Estrada Sandoval. "From my point of view I saw no relationship between him and Adnan. Why would you even help him?"

"You don't even know him like that, you know? It's not like Jen calling and needing help."

6. We learned Jay was known for telling lies.

In the documentary, several of Jay and Adnan's high school friends said Jay was known for telling lies and exaggerating stories.

"He would make you believe his shirt was green if it was blue," his former best friend, Jennifer Pusateri, explained.

"Jay picks and chooses what he wants to tell and at this point it's created such a mess," she later added.

"He played a sport and was social with people but he was odd," added one of the girls from the magnet program. "I now think of him as shady. I don't think I thought of him like that at the time."

"If Jay gets pulled over and you're in a car with him and he's dirty or he feels like there's a chance that he's going to go to jail, he's going to try to dump every responsibility for anything onto you," Jay's close friend Christopher Lee Baskerville claimed.

"He'll trade places with you in a heartbeat," he continued. "Which is why people don't talk to Jay anymore."

7. We found out Jay keeps getting away with stuff.

At the end of the episode, the two detectives ran Jay's name through civil litigation and criminal databases.

There were 25 police contacts. Only some of them led to arrests and even fewer led to convictions.

The charges included assault of a police officer and assault of a girlfriend. In most of these cases the prosecutors were reluctant to prosecute.

8. We learned more about Jay's violent past.

In the final moments of episode two, we hear from Jay's ex girlfriend, Nikisha Horton.

Nikisha talks about the night Jay violently attacked her and then attacked a police officer who tried to intervene.

"He can go from zero to 100 really, really fast," she says.

"He was intoxicated, we were arguing, and I left. He saw me gone and he snapped. I saw him in the middle of the road and he just hit me, hit me.

Jay wasn't prosecuted for any of this.

"I think he knows ways to manipulate the law. From what I've seen the times he got arrested and came back so quickly, no bail, no call, no nothing."

You can watch the first two episodes of The Case Against Adnan Syed on SBS on Demand now.