OJ Simpson's crimes didn't qualify for federal charges. There has to be a federal crime for it to be charged that way. I believe in this case LM crossed state lines committing these crimes. Not all high-profile crimes will fall under federal jurisdiction. In this case there was a federal grand jury that decided charges were warranted.
A criminal complaint was unsealed today charging Luigi Nicholas Mangione, 26, of Towson, Maryland, in connection with the Dec. 4 murder of UnitedHealthcare executive Brian Thompson in Midtown Manhattan. Mangione was taken into federal custody today and will be presented this afternoon in...
www.justice.gov
As alleged in the complaint, over the course of the last several months, Mangione meticulously planned the execution of Brian Thompson in an effort to initiate a public discussion about the healthcare industry. Mangione targeted the victim, tracked his whereabouts, and traveled from out of state to New York City, where the victim was scheduled to attend the company’s investor conference. After arriving in the city on Nov. 24, more than one week before the murder, Mangione performed reconnaissance in the area around the victim’s hotel and the conference venue where the victim was scheduled to speak. Using a false identification, Mangione checked into an Upper West Side hostel.