I am American and this was my first thought when reading the headline. “Why is the FBI involved?” I can understand the CIA, like you said. So weird but a sign of our times.
FBI is just "the police", so it's very normal and happens all the time that police experts from one country are invited to help investigate crime in another country.
When I hear CIA, I think coercion to collect information, most usually information to be used to coerce somebody else. When I hear FBI I think coercion to instigate what will be well-publicized conspiratorial crime. Actual espionage and investigation are decidedly secondary activities.
