The 15-year-old mystery of who killed Washington intern Chandra Levy is again an open question after prosecutors dropped charges against the man who once stood convicted of her murder.

A judge Thursday dismissed all charges against Ingmar Guandique after prosecutors said new developments left them unable to prove his guilt beyond a reasonable doubt. Prosecutors refused to discuss details of what led them to abandon their case.

Levy's 2001 disappearance became a national obsession after she was romantically linked to Gary Condit, then a Democratic congressman from California.

Condit was once was a suspect, but authorities eventually charged and convicted Guandique.

Last year, though, Guandique was granted a new trial after doubts emerged about a jailhouse informant who was the key witness at Guandique's initial trial.