The deadly office shooting in California involving a federal immigrations supervisor and a special agent is the latest mark against U.S. Immigration and Customs Enforcement, the law enforcement agency created after the 2001 terror attacks.

Its officers and agents have themselves been arrested for crimes, accused of improper relationships with informants, convicted in embezzlement cases, and more.

Insiders said ICE, which operates under the Department of Homeland Security, struggles to overcome internal friction and competing cultures among employees who worked at the different federal agencies that were combined nine years ago to form ICE: the former Customs Service in the Treasury Department and the Justice Department’s Immigration and Naturalization Service.