28 U.S. Code § 540B - Investigation of serial killings
(a) In General.— The Attorney General and the Director of the Federal Bureau of Investigation may investigate serial killings in violation of the laws of a State or political subdivision, if such investigation is requested by the head of a law enforcement agency with investigative or prosecutorial jurisdiction over the offense.
(b) Definitions.— In this section:
(1) Killing.— The term “killing” means conduct that would constitute an offense under section 1111 of title 18, United States Code, if Federal jurisdiction existed.
(2) Serial killings.— The term “serial killings” means a series of three or more killings, not less than one of which was committed within the United States, having common characteristics such as to suggest the reasonable possibility that the crimes were committed by the same actor or actors.