Until this week when civil-fraud charges were brought against Ernst & Young LLP for its role in the collapse of Lehman Brothers Holdings Inc., auditors had largely side-stepped blame for the financial crisis.

Yet auditors had to pass judgment on some of the practices that caused the big losses that led to government bailouts. The case against Ernst highlights the roles accounting firms played and raises questions about whether reforms enacted after the last financial crisis went far enough.

Auditors weren't involved in a lot of the primary causes of the crisis: bad lending and investing decisions; a lack of understanding of risk; and flaws in the credit-rating system. Auditing isn't meant to stop companies from making dumb business moves—just to make sure those moves are properly disclosed.

Accounting firms were at the center of the last financial crisis, when companies such as Enron Corp. and WorldCom Inc. collapsed amid scandals. New accounting rules focused on the abuses of the time, but touched on some of the issues in the Ernst case, including the relationship between companies and their auditors, the processes companies have in place to prevent fraud or errors in their financial statements, and the way companies value their assets.