Should suicide be considered superseding cause?

On November 4 at 10:00 am the Court of Appeals for the Seventh Circuit will hear oral arguments in case called Johnson v. Wal-Mart Stores Inc. the issue of which is whether, under the facts of the case, the decedent's conduct in committing suicide was a superseding cause that should relieve the defendant of liability. The alleged facts of the case are as follows: Wal-Mart Stores Inc. sold a woman firearm ammunition without asking her to produce an Illinois Firearm Owners Identification Card. Selling ammunition to anyone who does not have such a card is illegal under Illinois law. The woman did not have such a card because she had been a mental patient within the previous five years. After she purchased the ammunition, she returned to her residence, loaded a revolver and shot herself in the chest. She died the next morning. Her husband filed a wrongful death lawsuit against Wal-Mart and Wal-Mart replied by filing a motion to dismiss arguing the plaintiff's allegations did not meet the element of proximate cause because the suicide was an unforeseeable event that relieved Wal-Mart of liability for negligence in selling the ammunition. The lower court granted the motion to dismiss and the plaintiff appealed. The lower court's decision is reported in 587 F.Supp.2d 1027 (C.D.Ill. 2008).