Who is Adnan Syed? Here's what you need to know about the case chronicled by 'Serial' podcast

The podcast “Serial” exploded on iTunes in 2015 by re-examining a closed Baltimore murder case. The subject of that series, Adnan Syed, was granted a new trial by Maryland’s second-highest court in March. The decision stems largely from the failure to call a witness named Asia McClain who says she saw Syed the day of the murder at a local library.

On Friday, Maryland’s highest court reversed that decision.

Here’s what you need to know:

On January 13, 1999, an 18-year-old woman named Hae Min Lee went missing from Baltimore County. She was last seen driving away from Woodlawn high school in a gray Nissan Sentra.

Lee’s body was found a month later in Baltimore’s Leakin Park. She had been strangled.

Her ex-boyfriend, Adnan Syed, 17, was eventually charged in her killing — detectives pursued him as a suspect after an anonymous tip. Prosecutors said Syed had murdered her out of jealousy after finding out she was dating someone else. No physical evidence tied Syed to the crime, but a witness testified that he helped Syed bury her body. Syed never admitted to killing Lee.

In 2000, a jury found Syed guilty of first-degree murder, robbery, kidnapping and false imprisonment. He was sentenced to life in prison.

"I have maintained my innocence from the beginning," Syed said at his sentencing.

So did his family and friends.

Rabia Chaudry, a friend of Syed’s and author of “Adnan's Story: The Search for Truth and Justice After Serial,” previously told The Sun that she believes Syed's Muslim heritage blinded police and prosecutors to the holes in their investigation.

"They weren't able to find evidence that Adnan was a violent boyfriend or that he had a history of being abusive, so they had to plug in his religion as a substitute. They had to demonize an entire community by arguing that because Adnan is Muslim, he had the potential to do this."

Sarah Koenig, a former Baltimore Sun reporter, spent a year investigating the case for NPR’s “This American Life,” along with help from then-Sun reporter Justin George. The resulting podcast series, “Serial,” was downloaded millions of times and drew new attention to the case.

Koenig spoke to a former classmate of Syed’s and Hae’s named Asia McClain. Now McClain Chapman, she said she had seen Syed at the Woodlawn library the day of the murder. Chapman later testified in a sworn deposition and at a hearing on Syed’s case.

He was "completely normal," she said in 2016.

Chapman wrote a letter to Syed after his arrest in 1999, offering to help him if he thought the information would be useful in mounting a defense. She wrote a second letter a day later, she said, but never heard from Syed's defense.

Chapman's testimony wasn't heard at Syed's 2000 trial.

Syed was granted a post-conviction hearing in February 2016, during which his new attorneys argued that his original counsel had failed to call Chapman as an alibi witness. They also questioned the reliability of cellphone evidence used to place Syed at the spot where Lee's body was found.

Four months later, retired Judge Martin Welch, who had denied Syed's previous request for a new trial, vacated his conviction and ordered a new trial. The judge said questions about the cellphone tower evidence should have been raised by Syed's original team.

The Maryland attorney general’s office appealed Welch’s ruling in August 2016. In March, Maryland’s Court of Special Appeals upheld Welch’s ruling. And this week, Attorney General Brian Frosh’s office asked the Maryland Court of Appeals to reverse the lower court’s ruling to overturn Syed’s conviction.

The defense’s failure to call Chapman as a witness in 2000 played a key role in the March decision to grant Syed a new trial. In writing the Court of Special Appeals opinion, Chief Judge Patrick L. Woodward wrote that it was reasonable to think that Chapman’s testimony would have raised “reasonable doubt in the mind of at least one juror,” thus changing the outcome of the entire trial.

Syed’s first lawyer, Maria Cristina Gutierrez, died of a heart attack in 2004. She had resigned after the state Court of Appeals ordered her "disbarred by consent" in 2001 after allegations that clients' money slated for a trust account wasn't there. Gutierrez said she was too ill to practice law or fight the disbarment.

In 2016, Deputy Maryland Attorney General Thiru Vignarajah said notes from Gutierrez's case file determined that the "pursuit of Ms. McClain would not be a worthwhile endeavor.”

Vignarajah said Chapman’s account did not mesh with Syed's own account to police of his movements that day, and raised a number of "warning signs and red flags" that Gutierrez could reasonably have chosen to shy away from.

Chapman described participating in the "Serial" podcast unwittingly. She said she assumed it was a sparsely followed internet radio show. But her account became a crucial chapter in the 12-episode series, and she "binge-listened" to the program.