Most likely done by animal rights activists, I suspect they are all dead now as they have no black market value. See http://www.mystatesman.com/news/were-hu ... x5HJKnPMJ/
Ok, I think your anti-environmentalist sentiments are going a little too far. You are outright assuming that animal rights activists did this without any evidence. Stealing salamanders from a lab that is an insurance policy on the survival of several endangered species doesn't really fit their MO. Have their been any high-profile instances of animal rights activists taking extreme measures to "help" salamanders before? None come to mind, but I could be wrong.
I think it's far more likely that someone with knowledge of the lab (an employee or former employee?) helped facilitate this theft.
You are outright assuming it was an inside job of theft. Both of your ideas are just as viable a reason as any other given the amount of, or lack thereof details about the alleged theft. Actually if it was theft, and an inside job, it could be an inside job with the help of an activist. You would both be right.
My first thought was someone screwed up and they died somehow. My guess is that we will never find out what happened.