A lawyer for a radical Muslim convert imprisoned for supporting terrorism urged a federal appeals court Thursday to revive the man's parental rights lawsuit, which a judge had dismissed as frivolous.

Jason LaFond told a three-judge panel of the 4th U.S. Circuit Court of Appeals that Zachary Chesser's complaint against his mother and FBI agents, while lengthy and complicated, was not fanciful and was supported by numerous documents.

The judge who dismissed the lawsuit "didn't say whether it was factually or legally frivolous, but it was neither," LaFond said.

Court papers show that Chesser attempted to join the al-Shabab terrorist group in Somalia, taking his baby with him to the airport in an attempt to look less suspicious.

It didn't work. Chesser, who had attracted law enforcement attention after posting threats against the creators of "South Park" for cartoons he felt insulted the prophet Muhammad, was arrested and pleaded guilty in 2010 to attempting to support terrorist groups and threatening violence online. He was sentenced to 25 years in prison.