It's what I get for always picking it up on reruns.
I just now saw Judgement Day from season 5.
Lauren Holly's character, Jenny Shepard, was killed.
Turns out 9 years ago when she and Gibbs worked together, she couldn't kill her target.
So the target came back to get Gibbs, but first Decker was killed, then she sacrificed herself to protect Gibbs.
So it's all tidied up now, but DiNozzo, David and McGee are all being reassigned!
Now I have to look through the Season 5 and 6 info online to find out what's going on.