A man convicted of killing Washington intern Chandra Levy is expected to get a new trial after government attorneys on Friday said the “interests of justice” would best be served by one.

On Friday, after more than a year of sporadic hearings and legal wrangling, government attorneys withdrew their opposition to a new trial for Ingmar Guandique. In a four-page motion, they told a judge they were preparing to retry him.

Guandique’s attorneys had previously asked a judge to grant him a new trial because they said a key witness in the case, Guandique’s one-time cellmate, gave false or misleading testimony during his 2010 trial. Guandique’s attorneys said prosecutors knew or should have known the testimony was problematic and investigated further.

“The government continues to believe the jury’s verdict was correct,” prosecutors wrote in their motion, adding that they didn’t believe anything else learned during a post-trial investigation “casts doubt on the defendant’s guilt”.

However, prosecutors said that the “passage of time and the unique circumstances of this case” had made opposing a new trial more difficult.

“The interests of justice will therefore be best served by the government’s withdrawal of its opposition to the defendant’s motion and affording him a new trial,” prosecutors wrote.

One of Guandique’s attorneys, Jon Anderson, released a brief statement after the motion was made public.

“The government’s case against Ingmar Guandique was based on a lie,” Anderson said. “We are gratified that the government has now acknowledged that it cannot defend this conviction, and we look forward to justice being served in a new trial.”

Levy’s mother, Susan Levy, said in a telephone interview that she has always had some questions about whether Guandique killed her daughter, though her husband is “100%” convinced. She said that she wants to see justice done and ensure the right person is convicted, but she said a new trial wouldn’t make a difference in one important respect.

“It not going to make a difference for me, because my daughter’s dead,” she said.

Levy’s 2001 disappearance created a national sensation after the 24-year-old Modesto, California, native was romantically linked with then Representative Gary Condit, a California Democrat who was ultimately ruled out as a suspect.

Her remains were found in Washington’s Rock Creek Park in 2002, and prosecutors argued her death matched a pattern of attacks Guandique committed on female joggers. He was convicted and given a 60-year sentence, though he has maintained he is innocent.

At the center of Guandique’s new trial request was his former cellmate Armando Morales. Morales testified at trial that Guandique confided in him that he was responsible for Levy’s death. Because there was no physical evidence linking Guandique to Levy’s death, Morales provided some of the trial’s most powerful testimony.

In a court document filed in support of a new trial, however, Guandique’s attorneys suggested Morales lied several times at trial, including testifying he had not asked for anything in exchange for his testimony when, in fact, they say he asked to be put in a witness protection programme.

They also argued Morales, a former California gang leader, testified at trial that he didn’t know how to come forward with information to law enforcement when, in fact, he was an experienced cooperator who had previously provided information.

Prosecutors have said they learned about some of Morales’s cooperation with authorities about a year after Guandique was sentenced. In late 2012, they brought the issue to the judge who had overseen the case, and the information and subsequent investigation led to the new trial request. The latest hearing in the case had been scheduled for next week, but prosecutors asked for a hearing in two weeks. They said at that hearing they would tell the judge how long they need to prepare for a retrial.