Naio - check what kind of poison bait was used! There's a new type of bait they call "Second Generation" - the good news is that it's VERY efficient - the bad news is that it takes about a week to kill a rat or mouse; and if something eats the rodent during that time period (or even if it's dead) - THAT animal can die, too.
Here are the ingredients used and whether they are first or second generation (copied from Wikipedia)
First generation: warfarin, coumatetralyl
Second generation: difenacoum, brodifacoum,(6) flocoumafen and bromadiolone
I'm really fond of domestic rats - but having studied their wild cousins, as much as I don't like to kill wild things - they are incredibly destructive. I'd want them out, ASAP, before they start chewing on wiring, for example. I'd call a professional - and keep the cats away!
If they were in a "sealed" area, mothballs will usually drive out most critters, but being in the basement/crawl space of a house, gives them access to the entire house via plumbing, HVAC and wiring runs.