The remainder of the case is almost wholly unremarkable, in its way.
They bring Petty Officer Conrad in for further questioning the next morning, and she does not even ask them how the evidence led them back to her. Ziva is almost disappointed, in a way; she would have liked to see the look on the woman's face when they told her even magic is not untraceable.
Her motive is a bizarre mixture of the jealous lover and the betrayed friend - the betrayal seems to have been that the Navy wife wasn't interested in Petty Officer Conrad's advances. She is reluctant to tell them where she got the poison, until Tony points out that doing so might win her a lighter sentence; it seems Lieutenant Vickers was not far off the mark, when he speculated that she turned to the supply chain.
"What part of the supply chain would have that kind of thing?" Ziva says, after the interrogation is over.
Tony shrugs. "Like Vickers said. Someone who doesn't care about how legal it is, or why you're after what you're after. Or, hell, this is the same government that's considered making gay bombs for military use. Maybe it's part of the supply chain."
"It should not be, if it is. Something like that is an entirely unresponsible use of magic."
Ziva rolls her eyes. "I should think they mean the same thing. I did like Vickers' trick, though. That cannot be an easy thing to make, if it does so much."
"It'd be beyond me no matter how hard I tried. Always did suck at potions. I just can't believe it took us so long to figure out we weren't necessarily solving anything with the countercharms."
"I could've told you that, DiNozzo," Gibbs says, as he passes through on his way to the stairs.
Ziva sits upright, and frowns. "You could have - then why did you not?"
"You didn't ask."
Tony makes a few fish faces to rival McGee's from yesterday, then pounds his fist on his desk. "That's how you get those damn boats out of your basement, isn't it? I should have guessed!"
Gibbs goes on up the stairs without offering a response, and Ziva can't help but laugh.