NATIONAL BRIEFING / NATIONWIDE

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

According to documents obtained by the Associated Press, Immigration and Customs Enforcement agents have blundered in their dealings with informants and other sources, covering up crimes and even interfering in a police investigation into whether one informant killed another in El Paso.

The heavily redacted documents detail how one agent failed “to report murders . . . to her supervisor” and how another failed “to properly document information received from a confidential source in violation of ICE policy and procedure.”

Kelly Nantel, an ICE spokeswoman in Washington, said in an e-mailed statement that the agency “works with confidential informants in accordance with established best practices and guidelines of federal law enforcement agencies.”