"There is no dispute that every studio was aware of his true and legal name," Judge Elden Fox said throwing out the sole charge against Jason James Murphy.
On the state's Megan's Law list, where he was required to register because of his 1996 kidnapping of an 8-year-old, he was identified as Jason James Murphy with no aliases.
He was arrested in December following a Times report about how "Super 8" director J.J. Abrams and others in the industry had recently discovered Murphy's conviction.
He was charged with failing to comply with a part of the sex offender law that requires registrants to inform authorities of any name change within five days.
In his ruling, Fox expressed concern that parents of young actors who auditioned with Murphy could not find the name he used on his resume, e-mails and voicemail if they searched the sex-offender registry.
"I think parents who may be involved in this particular business probably should be aware of the fact that he is a 290 registrant," the judge said.
But, he said, the law didn't prohibit Murphy from using a shortened version of his legal name professionally and the fact he used his legal name on payroll sheets and tax forms made his criminal history available to his bosses.
"There was nothing the defendant did in this case to prevent that information from becoming public," Fox said.
His decision came a day after Murphy took the stand in Fox's Beverly Hills courtroom.
He said he had used Jason James as a stage name before his crimes and continued to do so because he was trying to build a body of work.
He told the judge he meticulously followed the sex offender laws because he never wanted to return to prison and hadn't considered his professional name an alias.
"I wasn't hiding it," he said.
After the judge's decision, Murphy left court smiling.
The revelations of his sex-offender status destroyed his career and he subsequently moved from Los Angeles to Seattle.
"It's unfortunate that Mr. Murphy lost his livelihood and hard-won career as a result of these charges, but he is determined to use his talents and skill to move forward with his life," his attorney, Shawn Holley, said outside court.