Next year will mark two decades since Adnan Syed was convicted of murdering his ex-girlfriend Hae Min Lee in Baltimore, Maryland.

He was 19 when he was found guilty of first-degree murder and sentenced to life in prison plus 30 years in 2000 for strangling Hae in a car park the previous year.

Syed, who has remained in prison ever since, maintains that he had nothing to do with the killing.

While his case received little coverage in the media at the time, it attracted international attention in 2014 when it was featured on the Serial podcast, which was downloaded millions of times and prompted legions of listeners to scrutinise the case online.

It jumpstarted a new era of true crime podcasts and TV shows dominating the mainstream.

Sky Crime’s Emily-Jayne Wilde summed up the phenomenon to Metro: “It allowed the listeners to unpick all this evidence and become the arm chair detective.

“Since then it continued to spiral and what was an episodic case has now become serialised. We consume it so readily with one case across multiple episodes like you would with a drama. Serial was the time when it all took off.”

What happened to Syed after the podcast?

Syed appealed his conviction on the grounds that his previous lawyer failed to call a key alibi witness, Asia McClain, who featured heavily in the podcast. He also questioned the reliability of mobile phone evidence used to place him at the spot where Hae’s body was found.

In June 2016, Circuit Court Judge Martin Welch granted Syed a new trial. The court found that Syed’s original trial attorney, the late Cristina Gutierrez, was ineffective by failing to cross-examine the prosecution’s cell tower expert about the reliability of location data for incoming calls. However, the State of Maryland appealed the ruling.

Syed’s lawyer filed a motion arguing that his client should be released from prison while he awaited the outcome of the appeal because he posed “no danger to the community” and had already served 17 years in prison “based on an unconstitutional conviction for a crime he did not commit”. This was unsuccessful.

Then in March last year, the Court of Special Appeals ruled in Syed’s favour, granting a new trial. It concluded that McClain’s testimony might have altered the “entire evidentary picture”, but dismissed the cell tower issue.

Again, prosecutors appealed the decision for a new trial and, in March this year, won their case in Maryland’s highest court, the Court of Appeals. The court ruled that Syed’s defence lawyer had been “deficient” in not calling a potential alibi witness to testify during the original trial but that ultimately Syed was not “prejudiced” by that deficiency.

What happens next?

Syed’s lawyer, Justin Brown, told The New York Times that Syed’s family were “devastated” by the Court of Appeals decision but vowed not to give up.

In August, they filed a petition to the US Supreme Court to take up his case and are now waiting to hear back.

Rabia Chaudry, an attorney and lifelong friend of Syed, said: “There are other steps. There are at least five or six options but we’re just going to do them one at a time because this will take years again.”

In the 42-page petition to the Supreme Court, Syed’s lawyers say the Court of Appeals decision “significantly discounts the importance of alibi witnesses, in clear conflict with numerous state and federal courts”.

What has Syed been doing in prison?

Serial presenter Sarah Koenig told Fresh Air podcast that he has entertainment available behind bars: “He has an Xbox, one of those game things for the TV, and apparently you can play a CD on it, so at one point I said, ‘I can burn [Serial transcripts] onto CDs for you and send you those’.”

She also said that Syed doesn’t have access to the internet, but is still able to keep up to date with news about himself.

Chaudry told a TCA panel in February: “Adnan hears everything about himself from the news. The guards keep him updated. He gets all the newspapers and magazines.”

He was also found in possession of a contraband mobile phone in 2009.

Undisclosed, a Serial follow-up podcast hosted by Chaudry, confirmed in 2015 that Syed had been married - and divorced - while in prison.