Hundreds of pages of confidential internal documents from the private equity firm Bain Capital published online Thursday provided new details on investments held by the Romney family’s trusts, as well as aggressive strategies that Bain appears to have used to minimize its investors’ and partners’ tax liabilities.

The documents include annual financial statements and investor letters circulated to limited partners in more than 20 Bain and related funds where Mitt Romney’s financial advisers have at times invested large parts of his personal fortune, estimated at more than $250 million.

As part of his retirement agreement with Bain, Mr. Romney has remained a passive investor in the company’s ventures and continues to receive a share of the firm’s investment profits on some deals undertaken after his departure.

The documents, obtained and published by Gawker.com, do not specify the stakes held in the funds by the Romney family trusts or by other investors. But they highlight the range and complexity of Mr. Romney’s investments at a time when those very qualities have been the subject of the Obama campaign’s main attacks against him, including demands that Mr. Romney release his tax returns to clear up any suggestion that he might be benefiting financially from legal loopholes or tax shelters.