Some experts on tax law say Mitt Romney's release of his 2011 tax returns Friday doesn't do much to shed light on his finances.

They say in order to reveal whether he used aggressive tax-deferral strategies, and what kind of tax advantages he's getting from his offshore investments, Romney would have to include returns dating back to his years at Bain Capital. Those returns would also reveal the source of his massive retirement account, and the details behind his $3 million Swiss bank account, which has now been closed.

Romney has said he will only provide the returns from the past two years.

His campaign says the returns from 2011 show that Romney and his wife paid an effective tax rate of 14.1 percent last year on income of $13.7 million. Much of the income is from investments held in a blind trust, and campaign aides have stressed that Romney makes no decisions on how the money is invested.

The man who oversees the blind trust says the Romneys could have claimed a higher charitable deduction last year -- but they limited that deduction to $2.25 million when they actually gave more than $4 million to charity. The trustee says if the Romneys had claimed more of a deduction, they wouldn't have complied with Romney's statement that he paid at least 13 percent in taxes each year.