SAN FRANCISCO (AP) — Federal prosecutors charged Texas billionaire Robert Brockman on Thursday with a $2 billion tax fraud scheme in what they say is the largest such case against an American.

Department of Justice officials said at a news conference that Brockman, 79, hid capital gains income over 20 years through a web of offshore entities in Bermuda and Nevis and secret bank accounts in Bermuda and Switzerland. Prosecutors announced that the CEO of a private equity firm that aided in the schemes would cooperate with the investigation.

The 39-count indictment unsealed Thursday charges Brockm...