Syed, whose story was chronicled in the hit Serial podcast, had previously had his conviction vacated in September.

The about-turn came after a judge vacated Syed’s conviction in September at the request of Baltimore prosecutors, on the basis that earlier prosecutors had not handed over evidence that could have affected the outcome of his case.

Syed had been convicted in 2000 of the murder of his ex-girlfriend Hae Min Lee a year earlier. He spent more than two decades fighting the verdict.

On Tuesday, the Appellate Court of Maryland ruled that the lower court had violated state law by not giving Lee’s family adequate notice of a hearing to vacate the conviction.

The court ruled that giving Lee’s brother, Young Lee, only one business day before the hearing was “insufficient time to reasonably allow Mr Lee, who lived in California, to attend” in person. He ultimately had to watch remotely.

The court said it was obligated to remedy the lower court’s violations “as long we can do so without violating Mr Syed’s right to be free from double jeopardy”.

“We can do that, and accordingly, we vacate the circuit court’s order vacating Mr Syed’s convictions, which results in the reinstatement of the original convictions and sentence,” the ruling said. It added that a new hearing to vacate Syed’s conviction will be held.

In asking the courts to toss Syed’s conviction last year, Baltimore prosecutors said they were not asserting the defendant was innocent. Instead, they asserted that they lacked confidence “in the integrity of the conviction” and recommended that he be released on his own recognisance or bail.

The prosecutors cited “undisclosed and newly developed information regarding two alternative suspects, as well as unreliable cell phone tower data” as reasons for vacating the conviction.

Those “alternative suspects” were known people at the time of the original investigation and were not properly ruled out nor disclosed to the defence, prosecutors explained.

The motion effectively put Syed in a new trial status, meaning his conviction would be vacated, but the case would remain active.

“Whether the state ultimately continues with a trial in this matter or dismisses the charges will depend on the outcome of the ongoing investigation,” the Maryland state attorney’s office said at the time.

Syed, who was 17 at the time of the murder, has maintained his innocence for decades.

His story captured the attention of millions in 2014 when the debut season of the Serial podcast focused on the case and raised doubts about some of the evidence, including mobile phone tower data.

Syed is not set to be taken back into custody following the most recent ruling, The Associated Press news agency reported.