The female lobbyist who was the subject of sexual boasting by former Assemblyman Mike Duvall issued her first public statement Monday, describing his allegations as untrue and her experience as a "professional and personal nightmare."

The statement from Sempra Energy lobbyist Heidi Barsuglia came in response to an announcement that the Justice Department would not file any charges over the conduct described in a legislative committee tape in which Duvall can be heard detailing sexual encounters with two lobbyists.

Sempra Energy also issued a statement saying its own investigation into the matter had concluded and that Barsuglia, who had denied any wrongdoing from the outset, would return to work.

"What is shocking to me and my family is that anyone would have taken seriously the statements of someone boasting about his alleged exploits or even believed for a moment that they were true," said Barsuglia, who was identified in an ethics complaint as the former lawmaker's mistress.

Duvall, a Republican from Yorba Linda, stepped down shortly after a recording surfaced in which he bragged during a break in a committee hearing about his sexual trysts. The married father of two laughed about having sex with and spanking one of two mistresses.

Ethics watchdogs immediately called for further investigation into the alleged relationship between Duvall and Barsuglia, who lobbies for a company that had business in front of a committee vice chaired by Duvall.

The U.S. attorney's decision not to pursue legal action marks an end to any investigative efforts.

Assembly Speaker Karen Bass' call for a full-blown ethics inquiry was sidelined after the Legislature's attorney said its ethics panel does not have the authority to investigate lawmakers who have stepped down.

The California attorney general's office and the Fair Political Practices Commission have also said they will not investigate the matter, citing insufficient evidence that the conduct described by Duvall broke any laws.

Derek Cressman, Western regional director for Common Cause, a government watchdog group that has called for further investigation into the tapes, said the outcome reflects a need for stricter rules governing the relationships between lobbyists and lawmakers.

"I think we are in a classic he-said, she-said situation, and the public may never know what actually happened here," Cressman said.

"With this phase of the scandal basically at a dead end, I think it now puts the ball back in the court of the Legislature to tighten the lobbyist disclosure rules," he said.

Barsuglia's attorney Malcolm Segal said Monday that his client has been "defamed in monumental proportions" by Duvall's comments, which he said were "a plain, old-fashioned lie."

"Her reputation, her job and her exemplary career have all been placed in jeopardy by Duvall's disgusting remarks," he said in a statement.

Duvall, who has said his resignation was not an admission of an affair but a reflection of "inappropriate storytelling," did not respond to a request for comment.

Segal said Barsuglia is considering "all of her legal remedies" for the damages suffered, but that there are no immediate plans to file a lawsuit against Duvall or any media organizations that named her in their reports.

"There's no question that her reputation has been seriously damaged, and she suffered an enormous personal and financial loss, but we want time to think about the future," he said.