Obama campaign adviser Robert Gibbs sees a pattern in GOP hopeful Romney's past of "outsourcing jobs" and offshoring his own personal investments -- and the only way for the former Massachusetts governor to prove that he isn't dodging tax laws is to release more tax returns.

During a Sunday interview with Gibbs, CNN host Candy Crowley noted that FactCheck.org had determined that an ad attacking Romney for outsourcing jobs while he was CEO of Bain Capital was false.

"We saw this a little bit again this week," Gibbs explained. "We've got a guy who believes and has been a pioneer in outsourcing jobs, and quite frankly he offshores most of his own personal investments -- presumably to shield them from taxes. Candy, I don't know about you, but I pick a bank because there's a ATM near my home, right? Mitt Romney had a bank account in Switzerland, he's got a shell company [in Bermuda]."

"He's done nothing illegal, right?" Crowley wondered.

"Nobody knows," Gibbs replied. "Nobody knows why he has a corporation in Bermuda, why he failed to disclose that on seven different financial disclosures, why he transferred it to somebody else's purview the day before he became governor of Massachusetts."

"The one thing he could do, Candy, to clear up whether or not he's done anything illegal, whether he's shielding his income from taxes in either Bermuda or Switzerland is to do what every other presidential candidate has done, and that's release a series of years of their own tax returns," the former White House press secretary continued. "Mitt Romney's father was the pioneer for releasing a series of tax returns. The best way to figure out of Mitt Romney's complying with American tax law is to have him release more of his tax returns."

"This is a guy whose slogan is 'Believe in America' and it should be 'Business in Bermuda.' That's what Mitt Romney is all about."