28 USC § 540B – Feds get qualified state,local immunity in serial killer cases

That's immunity from state and local laws in the course of the investigation of serial killers. It's presumed to be the temporary elimination of procedural and sovereignty limitations on police powers exercisable by federal LEOs. Although police can legally blow-up someone's house in the pursuit of a kidnapping suspect (sovereign/qualified immunity), they're not about to commandeer national guard tanks to run through some poor farmer's field looking for a serial killer. I think it might permit the legal theory for domestic drone assassination (Reaper-launched AGM-114R9X or AGM-114R) or sniper shot by executive order or supervising federal agent of a confirmed alleged serial killer who maybe planning or in the process of an imminent attack on a victim. (Exceedingly-rare circumstances but require legal footing for official actions that might be unconventional or technically illegal to protect the public. IIRC, the county sheriff is the supreme LEO of most lands. Some states and counties attempt to "nullify" federal LEA abilities by statute, which sets up a states' rights challenge in Constitutional gray areas.)