Dec. 19, 2011  -- When Mitt Romney faced questions on the campaign trail four years ago about investments in firms engaged in embryonic stem cell research, the presidential candidate had a ready explanation -- he was unaware because his vast financial portfolio was under the control of an independent trustee. Last week, Romney's campaign pulled out the same explanation when ABC News sought details about the candidate's holdings in the Cayman Islands, a notorious offshore tax haven.

"We remind you that Gov. Romney does not choose anything; these are BLIND TRUSTS," a campaign official wrote in an email.

But government ethics experts and election lawyers told ABC News that Romney's trust might not be quite as blind as he has long maintained. That's because Romney placed his quarter-billion dollar family fortune in the hands of his personal lawyer and longtime associate Bradford Malt.

Federal officeholders are required to either fully disclose all their financial holdings and any possible conflicts of interest, or place their holdings in a blind trust. Robert Kelner, a Republican election lawyer in Washington, D.C. with no ties to a current presidential campaign, explained the federal rules governing those blind trusts. "The Office of Government Ethics requires that a financial institution be appointed as the trustee and that the financial institution not be controlled by or have done business with the candidate," said Kelner. "It would preclude you from hiring your favorite lawyer as the trustee."

Romney was himself once skeptical of the notion that a politician could use a blind trust to preempt inevitable questions about his investment choices and potential conflicts. When he ran against Sen. Edward Kennedy in 1994, Romney spoke critically of Kennedy's claim that he had no control over his investments. "The blind trust is an age-old ruse," Romney told the Boston Globe at the time. But in 2003, as he prepared to take office as governor of Massachusetts, Romney placed his family's funds in his own blind trust to avoid whatever accusations could surface.

Romney's aides have referred to the blind trust in fending off political attacks about his investments ever since. In 2007, his GOP primary opponents took aim at several of his investments, including a stake in a firm that did business with Iran, shares of a Chinese oil company, and an interest in a company that engaged in embryonic stem cell research. Romney responded by announcing that Malt would take greater pains to insure Romney's investments would not conflict with his political views.

Last week, the issue surfaced again when ABC News sent the campaign questions about offshore investments. The campaign responded to the questions by explaining the Romney always paid his taxes on earnings from his investments in funds that had located outside the U.S. The campaign also emphasized that, regardless of the tax question, it would be unfair to hold the candidate responsible for investment decisions made by Malt, the trustee overseeing Romney's funds.

But some experts have questioned whether someone with Malt's close ties to Romney could oversee the candidate's finances with true independence. In addition to serving as the trustee for Romney's charitable foundation, Malt's law firm has represented Romney's interests in legal disputes, and Malt served as the primary outside counsel to Romney's company, Bain Capital. A sign of those ties surfaced in August, when Romney filed his financial disclosure report and revealed that Malt had invested over $1 million of the candidate's money in the Solamere Founders Fund. Solamere is managed by Tagg Romney, Mitt's son.

Cleta Mitchell, a Washington, D.C. election lawyer who has done legal work for Rick Santorum's campaign, said it would be hard to explain how Romney's independent investment fund would orchestrate a $1 million investment with his son's firm without violating the terms of a standard blind trust -- terms that typically prohibit communication with family members.

"What you're saying to the government is, I don't have any control over this, my spouse doesn't, and neither do my dependent children," Mitchell said. "The filer says, 'I don't know what's in it. I just get income from it.'"

Said one prominent campaign lawyer who has advised past Republican presidential candidates on these matters: "I don't see how this would provide the required trustee independence under the executive branch blind trust requirements."

Said another: "At the federal level, you have to have an absolute informational barrier and you're not supposed to influence anything with respect to the trust."

Neither Republican election lawyer would agree to be named, for fear of reprisals from the Romney camp.

In an email to ABC News, Romney's campaign acknowledged the arrangement does not live up to the strict standards for blind trusts established by the federal Office of Government Ethics. But the campaign was also quick to note that those rules do not apply to candidates for office -- they apply only to federal office holders.

"The blind trust does NOT meet the exacting 'federal blind trust' standard," a campaign official wrote in response to questions from ABC News. "We have never called it a federal blind trust. If Governor Romney is elected president, that will change."

Campaign officials said Romney set up the blind trust as he prepared to take office as Massachusetts governor, "so it meets different standards -- no less exacting, but different," adding that the trust was established in consultation with the Massachusetts State Ethics Commission. "Governor Romney received a written opinion from the State Ethics Commission that the blind trusts were effective," a campaign official said.

Massachusetts does not have a set standard for blind trusts, however, according to David Giannotti, an ethics commission spokesman. He said if the commission did issue an opinion to Romney giving its blessing to the governor's blind trust, it would be confidential and he could not discuss it.

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