If it’s not a terrorist thing and just a random killing, why would the FBI have jurisdiction?
If not to control the release of information?
They have jurisdiction, basically, when they say so. Thusly was it in Hoover’s day, too. Does anyone wonder why he stuck his nose in the Lindbergh kidnapping? Then again, for a long while they didn’t intrude on investigations of clear national importance. The Dallas police were the ones who nabbed Lee Harvey Oswald (and let him be killed). But if was hit or miss in the past, it’s less so now, and not just because of the endless federal laws. They can slap the words “national security” onto anything and who’s gonna say boo?