In the next scene, he shows Calleigh how to find hidden tampering by filling the plastic juice jug with water and seeing where the leak springs. This is why he's in charge. Calleigh points out, reasonably enough, "Sam Carver shoots a needle through plastic -- why not just pour the isotopes directly into the juice?" Horatio replies that it's because the Carvers didn't do it. After a Sorkinesque bout of echoing dialogue -- "The Carvers are innocent." "The Carvers are innocent." -- Horatio decrees that they're looking for someone who knows his way around a syringe. Well, that narrows it down.
Delko, in the meanwhile, is still working the money; he tells Horatio he found a bill with the impressions made from a credit card or bank card pressed tightly against it. If Delko can figure out what the numbers are, he can probably trace the account to the killer. Which killer isn't made clear -- let's just assume at this point that everyone's already linked Carl's death by cervical fracture with a side of radiation to Belle's imminent death by radiation poisoning. Horatio's quite pleased with Delko: "Eric, your genius knows no bounds. Nice going." As he leaves, Delko calls out that he'll be getting in touch with the credit card company. It should be fairly easy; different credit card companies have different four-number blocks at the beginning of their sixteen-number sequence, so all he has to do is remember which card issues which numbers starting with a specific sequence. (Note to the forum: Do not try to confirm this here on the boards; the last thing y'all need to do is to be rattling off part or all of your credit-card numbers in a publicly accessible place. Call your customer service rep instead.)
Cut to Horatio talking to Belle as she evidently parrots to him, "George Risher." Horatio helpfully points out, "CEO of Risher Pharmaceuticals." Belle reminds him that she knows who he is, what with her having a class-action lawsuit against him for contaminating groundwater and endangering a thousand homeowners. Then she gets a case of the vapors. Horatio goes from cop to concerned nice guy within seconds, asking if she's okay, then ushering her down to a bench and telling her, "You need to get some rest now. You need to spend some time with friends or family and let me handle this, okay?" Belle apparently isn't listening, because she asks, "Do you know Horatio was the first CSI?" Horatio replies, "He was the what?" Belle explains, "In Hamlet, when Hamlet was poisoned and dying, he asked his best friend Horatio to tell the world." Then that makes him the first tabloid reporter, as opposed to the first person to put together evidence and build a case. Horatio smiles and promises, "Okay, I'll tell the world. But first, I'll talk to Risher, and I'll call you later." Galvanized with purpose, he strides off, leaving Belle sitting on the bench and mulling over how much more real her death seems now that she's beginning to physically break down.