MANAGUA, Nicaragua (CNN) -- Nicaraguan prosecutors are appealing a court's decision that overturned an American man's conviction in the killing of his former girlfriend and set the stage for his release, officials said.
Magazine publisher Eric Volz's mother says she's concerned for his safety.
The office of Isadora Ibarra, prosecuting attorney, said she had left Wednesday to deliver the appeal to Granada.
Eric Volz, 28, of Nashville, Tennessee, remains in custody despite the Monday ruling by a Nicaraguan appeals court that he should be released immediately.
His attorney, Fabbrith Gomez, has said the Managua judge who sentenced Volz -- Ivette Toruno Blanco -- was stalling on signing court documents, holding up his release. Blanco has said the documents were incorrectly numbered and returned to Granada, Gomez said.
Volz was convicted in 2006 of raping and killing Doris Ivanez Jimenez and sentenced to 30 years in prison.
But 10 witnesses in the case testified or gave affidavits swearing that he was in his office in Managua, two hours away from the town where Jimenez was killed, at the time of her slaying. Watch how American ended up in Nicaraguan prison »
One man, however, testified that he had seen Volz in the town, San Juan del Sur, just after the time police believe Jimenez was killed.
That man, Nelson Danglas, was originally arrested in the slaying but received full immunity in exchange for his testimony against Volz. No physical evidence from the scene linked Volz to the slaying.
In addition to Volz, the same court convicted another man, Julio Chamorro, of the murder, although investigators never connected him with Volz.
When the verdict was reached in Volz's trial, a mob had gathered outside the courtroom chanting for his conviction.
Volz's mother, Maggie Anthony, arrived in Managua on Wednesday. She visited the Supreme Court in an attempt to talk to judges concerning the case, but said no one there would talk to her.
"According to Nicaraguan laws, my son should be free," she said after coming out. "I don't know why he is still a prisoner."
She told CNN she does not understand why her son is still in jail, but plans to visit the hospital and see him Thursday. Volz was hospitalized a few months ago for a variety of ailments.
From there, Anthony went to Granada, about 30 miles away, to the appeals court. There, magistrates were questioning the whereabouts of Volz's case file, although Blanco claimed she had returned it to Granada. A judge told CNN Blanco must deliver an answer within 24 hours.
Late Monday, Anthony told CNN it "should have been a day of joy, of justice and celebration. But instead we're more fearful for his life right now than we ever have been. We're so frightened for him."
Volz founded and served as publisher of EP (El Puente) magazine, a travel lifestyle publication. E-mail to a friend
CNN's Edmundo Garcia contributed to this report.
All About Nicaragua