This episode explores the story of Adnan Syed, who may or may not have been wrongly convicted in 1999 of killing Hae Min Lee, Syed's ex-girlfriend who was a senior at Baltimore County's Woodlawn High School. She disappeared in January 1999. Serial's investigative team "follows up on long-dormant leads, rechecks alibis, and questions assumptions."[24] Host Sarah Koenig reveals that the story is in process and that she doesn't know how it will end

Adnan Syed and Hae Min Lee had a storybook romance, kept secret from their disapproving parents. When Lee broke it off, their friends had conflicting interpretations of Syed's behavior: he was either cool with it and sad, or in a rage and hatching a sinister plot to kill her. Syed consistently proclaims his innocence, but there are puzzling inconsistencies in the set of facts he tells.

Lee had been missing for three weeks when a man on his lunch break, referred to as "Mr. S", discovered her body. His account of how he found her body seems suspicious to detectives MacGillivary and Ritz, who questioned him, and his background check reveals some bizarre behaviors, including a series of streaking episodes.

An anonymous caller leads detectives to subpoena Adnan Syed's cell phone records. As a result, the detectives discover calls to Jen, who is a friend of one of Adnan's acquaintances, a weed dealer named Jay. Detectives interview Jen and then Jay, who says Syed told him he killed Lee, and then forced him to help bury her body. Details of Jay's story shifted in some significant ways over four interviews, but the detectives said they were able to corroborate his story using cell phone records.

Producers Koenig and Chivvis test drive the prosecution's route and timeline of Lee's murder between 2:15, when school let out at the high school, and 2:36, when Jay said Syed called him for pick up in the Best Buy parking lot and then showed Jay Lee's body in the trunk of her car. While that timeline seems possible, though just barely, evidence from the call logs and records of cell tower pings do not quite align with Jay's testimony about the rest of the afternoon.

In addition to Jay's testimony, evidence against Adnan Syed included a palm print on a map that could not be dated, and cell phone records. Did Syed ask Lee for a ride after school to get into her car? Koenig goes through all the evidence, including the prosecution's timeline and "some stray things" that don't add up, including a neighbor's story, the testimony of Jay's friend Jen, and the sequence of cell phone calls after Lee disappeared.

Deirdre Enright, Director of Investigation for the Innocence Project at the University of Virginia School of Law,[27] and a team of law students analyze the case against Adnan Syed. Deirdre thinks the evidence against him was "thin". She advises Koenig to keep revisiting all the evidence, allowing uncertainties to remain until there is a tipping point when her questions are resolved. They start with a presumption of Syed's innocence, and ask whether they can discover who really did kill Lee. They find some undeveloped forensic evidence, but Koenig is still uncertain.

How credible was Jay's story? Koenig interviews a jury member, who said Jay seemed like a nice young man and believable. A professional detective says the investigation of Lee's murder was better than average, and Jay had handed the police the case on a platter. Koenig and Snyder visit Jay, who declines an interview. Jay's friend Chris recalls what Jay told him about the murder, a story not consistent with Jay's courtroom version. Why did Jay agree to help Syed? Did Syed coerce Jay and threaten to hurt Jay's girlfriend Stephanie? His friends said Jay had a reputation for lying, but not about important things. Jay's friend Jen says she could understand why Jay might lie about some details, but she believed his story. Back to the question: what was the jury thinking?

Koenig reveals she has new information about the call at 2:36. First, Laura claims there were never any pay phones in front of the Best Buy, but Jay's drawing shows a phone booth in front of the Best Buy, and he claimed Syed was standing by that phone booth with red gloves on. Second, Lee's friend Summer says that Lee could not have been dead by 2:36, because she had a conversation with Lee between 2:30 and 2:45. Others also saw Lee after school that day. Third, Asia saw Syed at the library in that same time frame. Sarah Koenig explores Syed's perspective as he was questioned, arrested, tried, and sentenced, as well as his letters to friends about life in prison. She mentions that she has reasonable doubt, not in the legal sense, but in the "normal person" sense.

Did anti-Muslim sentiment affect the prosecution? The prosecution argued that Syed's community would help him flee to Pakistan if bail were granted, using stereotypes to make the case that Syed murdered Lee as an honor killing. Defense attorney Cristina Gutierrez argued that someone else did it, and police did not look beyond Syed. His first trial ended in a mistrial, and in the second trial she cast suspicion on Mr. S and Jay as involved in the crime, but she did not present a clear outline of these arguments or scrutinize discrepancies in the call log timeline. Gutierrez discovered the prosecutor had secured an attorney for Jay – arguably a "benefit" worth money – in connection with his pleading guilty as an accessory and agreeing to testify, but the judge did not agree that this tainted Jay's testimony. Koenig does not believe Cristina Gutierrez intentionally bungled his defense, but within a year after Syed's trial, Gutierrez became very ill, her career collapsed, and she was disbarred. Syed has a petition before a higher court which requires a response by January 14, 2015, on the narrow issue of inadequate defense of counsel based on Gutierrez not seeking a plea bargain, which Syed claims he had asked her to do. Because Syed has maintained his innocence, however, and therefore shows no remorse, he is unlikely to be paroled.

Koenig investigates negative rumors about Syed, though the rumors do not directly connect him to Lee's murder, and the most troubling rumors cannot be substantiated. People from his mosque were scared when he was arrested, some describing his story as a cautionary tale. Some believe Syed was duplicitous, capable of committing the crime. One rumor, that he stole money from the mosque, was partially confirmed by four people. Syed admitted taking some money when he was in eighth grade, but his mother found out, and he felt ashamed. Syed had a reputation as a peacemaker, "a good guy", helpful and caring. People who knew him in high school cannot believe he planned Lee's murder. Did Syed "lose it", and nurse feelings of rejection? Could Syed have committed murder in a dissociative state, not knowing he did it? Koenig explores whether Syed has true empathy or anti-social characteristics, and consults with psychologist Charles Ewing, who has interviewed many young murderers. Why does Syed not sound more angry about Jay or other people connected to his case? In an 18-page letter to Koenig, Syed reveals his concern about being perceived as manipulative, and says it doesn't matter how the podcast portrays him.

After spending over a year researching the case, Koenig still is uncertain what happened the day that Lee disappeared. She reveals new information that happened as a result of people hearing about the podcast: she has spoken with Don, Lee's boyfriend of 13 days at the time of her disappearance, and with Jay's former co-worker, Josh. Koenig reviews the phone records again with her production team and determines that neither Jay's nor Syed's story of that day aligns with the evidence. Unresolved discrepancies also include Jen and Jay's stories about how they disposed of Jay's clothes and boots. Reviewing possible motives for the murder, Koenig and her producers reason that logically, if Syed is innocent, he had extraordinarily bad luck because of circumstantial evidence involving him. Lawyers from the Innocence Project announce they will seek court approval to test the DNA found on Lee's body and a bottle found nearby, possibly pointing to another man, and Syed's petition in the court of appeals is still alive. Koenig expresses her desire to avoid unsubstantiated speculation and to focus on only the facts. She concludes that from a legal perspective, she would have voted to acquit Syed, although she still nurses doubts.

Sarah Koenig ducks back into the Adnan Syed case for a few days. There’s a hearing in Baltimore—a court proceeding that’s been nearly sixteen years in the making. Syed’s attorney will introduce new evidence, and present a case for why his conviction should be overturned. Sarah and producer Dana Chivvis will discuss what happens, day by day.

Sarah Koenig ducks back into the Adnan Syed case for a few days. There’s a hearing in Baltimore—a court proceeding that’s been nearly sixteen years in the making. Syed’s attorney will introduce new evidence, and present a case for why his conviction should be overturned. Sarah and producer Dana Chivvis will discuss what happens, day by day.

Sarah Koenig ducks back into the Adnan Syed case for a few days. There’s a hearing in Baltimore—a court proceeding that’s been nearly sixteen years in the making. Syed’s attorney will introduce new evidence, and present a case for why his conviction should be overturned. Sarah and producer Dana Chivvis will discuss what happens, day by day.

It’s Baltimore, 2022. Adnan Syed has spent the last 23 years incarcerated, serving a life sentence for the murder of Hae Min Lee, a crime he says he didn’t commit. He has exhausted every legal avenue for relief, including a petition to the United States Supreme Court. But then, a prosecutor in the Baltimore State’s Attorney’s office stumbled upon two handwritten notes in Adnan’s case file, and that changes everything.