Warner Bros.’ DC Comics wing has scored a legal win in its long-running battle over control of Superman rights with the estates of Man of Steel creators Jerome Siegel and Joe Shuster.

In a ruling issued Tuesday, the U.S. 9th Circuit Court of Appeals denied an effort by attorney Marc Toberoff, who reps the Siegel and Shuster heirs, to assert attorney-client privilege over documents that DC Comics claims are key to the litigation involving control of the famed superhero.

The three-judge panel ruled unanimously that Toberoff cannot assert the privilege because he had already disclosed the documents to the government as part of its criminal investigation of a lawyer, David Michaels, who briefly worked for Toberoff “before absconding with copies of several documents from the Siegel and Shuster files,” the ruling states. The appellate judges later amended their opinion and made clear that “there has been no finding of wrongdoing on the part of Mr. Michaels.”

The documents in question are a letter and other materials that Michaels sent to execs at DC Comics in an effort to “detail Toberoff’s alleged master plan to capture Superman for himself,” the ruling states. DC Comics execs gave the material to an outside attorney but then sought to obtain them as evidence through discovery motions in two other ongoing Superman cases.

Toberoff fought the disclosure, spurring DC Comics to file a separate lawsuit against him in 2010. Toberoff has maintained that while the documents were given to federal prosecutors as part of their investigation of Michaels, that decision amounted to a “selective waiver” of attorney-client privilege. Last year, a district court ruled in favor of the disclosure of the documents to DC Comics.

Warner Bros. believes the documents are central to proving its assertion that the Siegel and Shuster heirs had reached a settlement agreement with the studio in 2001, before Toberoff entered the picture as their lawyer and a prospective producer of future Superman properties. Appeals in that case, filed by DC Comics in 2004, are pending before the 9th Circuit.

The disclosure ruling comments on Toberoff’s dual role as a lawyer and business partner of the Siegel and Shuster heirs.

“The ethical and professional concerns raised by Toberoff’s actions will likely occur to many readers, but they are not before this court,” it states.

In a statement, Toberoff said: “We cooperated with the U.S. Attorney’s office to enable them to investigate the theft from our law firm of the Siegels and Shuster’s privileged documents. We are disappointed in today’s decision which holds that such cooperation with law enforcement by the victims of a privacy crime, itself waives privilege as to stolen documents. However, nothing in this ruling or the documents at issue will affect the merits of this case. We are considering our options as to the ruling, and will continue to vigorously defend our clients’ rights.”