(CNN) — Baltimore prosecutors on Tuesday dropped all charges against Adnan Syed, the man who spent over two decades behind bars for the 1999 killing of his ex-girlfriend Hae Min Lee and whose murder case was featured in the landmark podcast “Serial.”

Baltimore City State’s Attorney Marilyn Mosby said Tuesday she instructed her office to dismiss the charges after results of advanced DNA testing from Lee’s shoes ruled out Syed.

“The items that we tested had never before been tested,” Mosby said. “We used advanced DNA to determine that it was not Adnan Syed.”

She said the responsibility for the conviction belonged to past administrations, though she still apologized to Lee’s family as well as to Syed and his family.

“Equally heartbreaking is the pain and sacrifice and trauma that has been imposed not just on (Lee’s) family, but Adnan and his family, who together spent 23 years imprisoned for a crime as a result of a wrongful conviction,” she said.

Syed was freed from prison last month after prosecutors without warning moved to vacate his murder conviction, saying they no longer trusted it. Prosecutors had 30 days to decide whether to pursue a new trial and were waiting on DNA analysis to determine their next steps.

The decision to drop charges comes about 23 years after the disappearance of Lee, Syed’s ex-girlfriend and high school classmate. Her strangled body was discovered in a city forest three weeks later.

Syed, who was 17 at the time of her death, was charged with her killing, convicted in 2000 of first-degree murder, robbery, kidnapping and false imprisonment and sentenced to life in prison.

Yet he has long maintained his innocence, and his story was featured in the “Serial” podcast that raised questions about the conviction and his legal representation. The podcast reached a huge audience and set off a true-crime podcasting boom as well as further examinations of the case, including the HBO docuseries, “The Case Against Adnan Syed.”

Last month, prosecutors moved to vacate Syed’s murder conviction following a nearly yearlong investigation. Mosby said prosecutors were “not asserting, at this time, that Mr. Syed is innocent” but that the state “lacks confidence in the integrity of the conviction.”

The reinvestigation of the case revealed evidence about the possible involvement of two suspects other than Syed that was not properly turned over to defense attorneys, prosecutors said. The reinvestigation also raised questions about the reliability of cell phone data records, which were used to corroborate testimony of a witness who said he helped Syed dig a hole for the victim’s body.

Based on the prosecution’s motion, a judge last month vacated the conviction and freed Syed, who walked out of the courthouse to cheers and applause from supporters. He was ordered to wear an ankle monitor with tracking, according to Becky Feldman, chief of the Sentencing Review Unit of the Baltimore City State’s Attorney’s Office.

Erica Suter, Syed’s attorney and director of the Innocence Project Clinic, praised the decision to drop charges as long overdue.

“Finally, Adnan Syed is able to live as a free man. The DNA results confirmed what we have already known and what underlies all of the current proceedings: that Adnan is innocent and lost 23 years of his life serving time for a crime he did not commit,” she said in a statement.

“While the proceedings are not completely over, this is an important step for Adnan, who has been on house arrest since the motion to vacate was first granted last month,” she added. “He still needs some time to process everything that has happened and we ask that you provide him and his family with that space.”

Why prosecutors dropped charges

The path to Syed’s release began in earnest last April, when attorneys for Syed brought the case to the attention of the Sentencing Review Unit. A recent piece of legislation had allowed people convicted of crimes as juveniles to ask for a modified sentence after they have served 20 years in prison, Mosby’s office said.

That review revealed deeper problems with the case against Syed, though.

In particular, the prosecution discovered alternate suspects who were known at the time of the original investigation “and were not properly ruled out nor disclosed to the defense,” according to Mosby’s statement. The state has not disclosed the names of the suspects but said that, according to the trial file, one of them said, “He would make her [Ms. Lee] disappear. He would kill her.”

The investigation also revealed that one suspect was convicted of attacking a woman in her vehicle, according to the statement. The second suspect was convicted of engaging in serial rape and sexual assault, the statement said.

Lee’s car was located “directly behind the house of one of the suspect’s family members,” the statement said.

Prosecutors said they will continue to fight for justice for Lee’s family.

“We truly empathize with Hae Min Lee’s family, who believed they had resolution and are now being re-traumatized by the misdeeds of the prior prosecutors,” Zy Richardson, director of communications for the Office of the State’s Attorney for Baltimore City, said in a statement.

“As administrators of the criminal justice system, our responsibility is to ensure that justice is done, and the right person is held accountable. We refuse to be distracted from this fundamental obligation and will never give up in our fight for the Lee family,” Richardson said.

Lee’s familly has said they were not notified in a timely manner of the prosecution’s intent to vacate the charges. Young Lee, the victim’s brother, said he felt “betrayed” by the state.

“This isn’t a podcast for me, it’s real life,” Lee said during last month’s hearing.

Lee family attorney Steve Kelly said the family was not asking for Syed to remain in custody, but they did want to see the new evidence.

“If the wrong person has been behind bars for 23 years, the Lee family and the rest of the world want to understand what new evidence has led to that conclusion,” Kelly said.

“If Mr. Syed has been wrongfully convicted for Hae Min Lee’s murder, the state of Maryland would need to take responsibility for that extraordinary miscarriage of justice and would need to do everything possible to bring the actual killer to justice. The Lee family deserves at least that much,” he added.

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