Johnson & Johnson, hoping to reverse a $502 million verdict, is accusing plaintiffs attorney W. Mark Lanier of lying to a federal judge and jury about payments he made to two expert witnesses in a pivotal hip implant trial last year in Dallas.

The allegations against the Houston lawyer surfaced in documents unsealed this week by the U.S. Court of Appeals for the Fifth Circuit, which is hearing Johnson & Johnson subsidiary DePuy Orthopaedics Inc.'s appeal of the verdict. In an April 18 appeal brief, Johnson & Johnson lawyers Paul Clement and John Beisner said a “strange thing happened” when they started deposing the experts for a subsequent trial: The plaintiffs turned over checks written out to the experts, both of whom Lanier had insisted were not compensated for their testimony.

“Plaintiffs' concealment of the fact that two critical expert witnesses had been paid or expected to be paid—at the same time their volunteer status was trumpeted to the jury and used to evade the expert-report requirement—deprived defendants of their ability to fully and fairly defend themselves,” they wrote.