Which agency investigates violations of federal laws not assigned to other agencies?

The Federal Bureau of Investigation (FBI) is tasked with investigating violations of federal laws that are not specifically assigned to other agencies. This includes a wide array of criminal activities such as cybercrime, terrorism, public corruption, civil rights violations, and organized crime. The FBI serves as a principal federal investigative agency and an intelligence organization, enhancing its role in safeguarding national security and upholding federal laws.

Other agencies have more specialized focuses; for example, the Environmental Protection Agency (EPA) concentrates on environmental laws, while the Drug Enforcement Administration (DEA) primarily deals with controlled substances and drug-related crimes. The Department of Homeland Security (DHS) has a broad mandate primarily related to national security, immigration, and border management, but it does not have the same general law enforcement authority across all federal statutes as the FBI. Thus, the FBI’s overarching jurisdiction enables it to handle a variety of federal law violations, making it the correct answer in this context.