The Rookie: Feds S01 E21 Bloodline (II)

"The FBI has a new secret weapon."

The FBI takes on a case from LAPD involving a serial murderer who has been leaving limbs across state lines. After the team follows a lead from Antoinette and Elena's forensic breakthroughs, the killer retaliates against Laura. The crossover starts on The Rookie S05E21 Going Under (I).