CBS

Season 1: Episode 14 - LD50

LD50: A warehouse with five dead bodies, two of whom were apparently Marines, draws the attention of NCIS.  The "Marines" were wearing authentic uniforms, but weren't Marines, so NCIS is intending to oversee the investigation to make sure there is no military connection, however, when the cause of death is determined to be Botulinum poisoning, NCIS:LA takes on the case because Botulinum is a deadly neurotoxin and bio-weapon.  Sam and Callen pursue their first lead, an elderly woman suffering from Alzheimer's -- turns out she was a military chemist and she was approached by people she thought were Marines to help them isolate, purify and weaponize the toxin.  Though her disease makes her an unreliable witness, the rote memory of her job has not been destroyed and she successfully produces enough biotoxin to kill millions of people.  Callen recognized one of the dead bodies as a former security guard for Dallas (from Breach, the strip club owner with high-powered connections) and through him, they discover that a weapons dealer named "The Dutchman" is holding an auction for the poison.  Sam goes undercover as an interested buyer, and discovers there's going to be a demonstration at the Beverly Center.  Callen and Kensi race to the location and manage to thwart the attack.