BY MICHAEL RAPOPORT

Allegations that several former Credit Suisse Group AG employees misstated bond values revive a thorny question for investors: whether to trust the valuations companies assign their riskiest, most-illiquid assets.

Two former Credit Suisse employees pleaded guilty Wednesday to working to overstate the values of mortgage-backed securities owned by the firm, in an effort to boost their bonuses. A third ex-employee also faces a criminal charge, and all three men plus a fourth face a Securities and Exchange Commission lawsuit alleging that they fraudulently overstated the prices of $3 ...