SAN FRANCISCO — An up-and-coming federal prosecutor squared off Tuesday against a hardened defense veteran in one of the rare pharmaceutical fraud cases to hit a jury.

W. Scott Harkonen, former CEO of Brisbane-based biotech InterMune, concocted a press release that made false statements about the efficacy of his company’s star drug, Assistant U.S. Attorney Ioana Petrou said in her opening statement. And while Harkonen had ample opportunity to correct his behavior, instead he concealed it, she said.