For weeks, President Obama's top campaign strategists have tried to establish that Mitt Romney was at the helm of Bain Capital when some of its companies moved workers overseas.

Proving his presence at Bain between 1999 and 2002 would create a direct link to what Obama's team describes as the outsourcing of U.S. jobs. And it would contradict Romney's repeated assertions that by then he had left Bain, the private-equity firm he founded, to rescue the Salt Lake City Olympics.

But definitive proof about Romney's activities remains elusive, leading to another day of increasingly bitter charges and countercharges from the two campaigns.

On Thursday — even as Romney started broadcasting a television commercial accusing the president of approving dishonest attacks — Obama's campaign seized on a Boston Globe report about Securities and Exchange Commission (SEC) documents that show Romney was listed as chief executive, president and owner of Bain Capital during that period.

The president's team moved with a fury, holding a 45-minute conference call with reporters to denounce what they called Romney's "Bain lie." Stephanie Cutter, a deputy campaign manager for Obama, said Romney potentially had committed a felony.

"Either Mitt Romney, through his own words and his own signature, was misrepresenting his position at Bain to the SEC, which is a felony," Cutter said, "or he was misrepresenting his position at Bain to the American people."

The highly charged accusation again put Romney and his allies on the defensive — a position that already has caused consternation among his supporters. Matt Rhoades, Romney's campaign manager, issued a blistering statement calling on Obama to apologize for Cutter's remarks.

"President Obama's campaign hit a new low today when one of its senior advisers made a reckless and unsubstantiated charge to reporters about Mitt Romney that was so over the top that it calls into question the integrity of their entire campaign," Rhoades said in a statement.

He called Cutter part of an "out of control" staff working on Obama's behalf.

Yet, even as Obama's campaign continued to trumpet the Globe's disclosures, other reports emerged to support the Romney campaign's assertion that he did not have any operational control over Bain after 1999.

A statement from Charlyn Lusk, a spokeswoman for Bain Capital, reiterated Romney's position that he "has had absolutely no involvement with the management or investment activities of the firm or with any of its portfolio companies since the day of his departure" in 1999.

Lusk said that "due to the sudden nature of Mr. Romney's departure, he remained the sole stockholder for a time while formal ownership was being documented and transferred to the group of partners who took over management of the firm in 1999."

"Accordingly," she added, "Mr. Romney was reported in various capacities on SEC filings during this period."

Documents obtained by Fortune magazine Thursday appeared to bolster that contention. The magazine reported on its website that it had obtained offering documents for funds that Bain Capital circulated in 2000 and 2001. The documents listed the managers of the funds. Romney's name was not on them.

"Then there is Bain Capital Venture Fund — the firm's first dedicated venture-capital effort — whose private placement memorandum is dated January 2001," the magazine wrote. "Romney also isn't listed among its 'key investment professionals,' or as part of its day-to-day operations or investment committee."

However, James Cox, a Duke University securities-law professor, said the SEC's Schedule 13D forms always have been under legal scrutiny by SEC officials and company executives. He said law firms hired to file such reports — known as "beneficial ownership reports" because they deem who can sell securities — "pay great attention to these forms. I don't find that these parts of the documents are casually reported."

"It's hard for me to believe you could be listed as 'management anything' without it taking up a bulk of your time," said Cox, who had not reviewed Bain's statement Thursday.

Romney for years has said that he no longer was actively involved in Bain's operations once he left the firm. (As a presidential candidate, however, he continues to claim credit for job growth years later at companies that Bain had invested in.)

A biography of Romney published this year by The Boston Globe also seems to back up that account. Globe reporters described Romney's departure from Bain Capital in 1999 as "not so neat" and said he and his partners "squabbled over how the firm would operate without him."

The authors said a power struggle ensued over Romney's departure and described him as kneeling on the floor with one of his partners to pray for the business' survival. "We were facing a crucial event that threatened the very existence (of) our firm's partnership," said Bob Gay, the partner.

There has so far been no contemporaneous evidence of Romney's active participation in management decisions during the period in question. No one has come forward to produce notes of meetings that Romney attended. There is no indication of conference calls or partnership meetings in which he was involved.

Asked about the lack of such evidence, Robert Bauer, chief counsel for Obama's campaign, hinted that something like that might yet emerge.

"I would stay very much tuned on that," he said, adding that Romney could ask Bain Capital to release notes of meetings during that period.

If more reports establish that Romney has been less than truthful about his time at Bain, the political damage to his presidential bid could be lasting. The issue plays into a larger storyline that the president's team is trying to create: that Romney is hiding things about his past and his wealth.

But Romney's new television ad suggests a possible danger for Obama as well if voters conclude the president has crossed an ethical line. In the ad, Secretary of State Hillary Rodham Clinton is seen angrily denouncing Obama during the 2008 Democratic nominating contest.

"Shame on you, Barack Obama," Clinton says.

Information from The Associated Press is included in this report.