The Federal Bureau of Investigation is now part of the investigation looking into the deadly ambush of the joint patrol of U.S. and Nigerien forces in Niger earlier this month, which took the lives of four American soldiers.

Although it is not typical for the FBI to be involved with an investigation regarding a military operation, it isn’t unprecedented, FBI officials told the Wall Street Journal. The FBI has not taken over the investigation, even though it has the authorization to do so.