As somebody else said, you definitely need to let whoever is investigating know this, so they can check into whether these salt shakers are still available to test.
I'm also wondering, after you describe her checking the salt shakers, whether the incident at Thanksgiving where so many people got sick, was inadvertent due to her mistaking a "dirty" salt shaker with a "clean" one? Not that it makes a difference in the end, but it might explain why her M.O. on that one seems so different from the more pointed incidents when a single individual was targeted.
I think that the FBI skipped searching for salt, and went straight for what's in bodies. (Sounds morbid...) I am not sure why. I do know that since roy was looking through his cabinets and had his spices out, that maybe landauxvassie and cforgy should take a peek in those to see if anything unusual looking is still around that house. I searched my mom's house twice after that incident where I caught her with them, and all the shakers had vanished...no where to be found. I looked everywhere except her room because I couldn't get to that location with bruce in there all the time.
I do think that some people just got sic, but not intentionally targeted, as something specifically prepared for bruce may have been eaten by others, or the shake of the wrong shaker could've happened for sure. People stopped throwing up there so much after Bruce stopped throwing up so much, so there is a correlation.