One immigration agent was accused of running an Internet pornography business and enjoying an improper relationship with an informant. Another let an informant smuggle in a group of illegal immigrants. And in a third case, an agent was investigated for soliciting sex from a witness in a marriage fraud case.

These troubling misdeeds are a sampling of misconduct by federal Immigration and Customs Enforcement personnel as the agency seeks to carve out a bigger role in the deadly border war against Mexican drug gangs.