After Hosni Mubarak’s younger son, Gamal, left his job as an executive with Bank of America in London in the mid-1990s, he joined forces with Egypt’s largest investment bank. Today he has a significant stake in a private equity company with interests throughout the Egyptian economy, from oil to agriculture to tourism, corporate records and interviews show.

During President Hosni Mubarak’s nearly 30-year rule, he and his family were not flamboyant with their wealth, particularly by the standards of other leaders in the Middle East. While there is no indication that Gamal Mubarak or the bank were involved in illegal activity, his investments show how deeply the family is woven into Egypt’s economy.

Now with Hosni Mubarak out of power, there are growing calls for an accounting to begin.

Within hours of Mr. Mubarak’s resignation on Friday, Swiss officials ordered all banks in Switzerland to search for — and freeze — any assets of the former president, his family or close associates. In Egypt, opposition leaders vowed to press for a full investigation of Mr. Mubarak’s finances.

Tracing the money is likely to be difficult because business in Egypt was largely conducted in secret among a small group connected to Mr. Mubarak.