Rather than asserting that Goldman misrepresented a product it was selling, the most commonly used grounds for securities fraud, the Securities and Exchange Commission said in a civil suit filed Friday that the investment bank misled customers about how that product was created.

It is the rough equivalent of asserting that an antiques dealer lied about the provenance, but not the quality, of an old table.

To a layperson, the case against Goldman may seem clear cut.

After all, investors did not know some information about the product that they might have considered vital, and they lost $1 billion in the end. But the rules that govern these kinds of transactions are not so plain.

Several experts on securities law said fraud cases like this one, which focuses on context rather than content, are generally more difficult to win, because it can be hard to persuade a jury that the missing information might have led buyers to walk away.  More from The New York Times here.