Wow! What a crazy twist. To decrease risk, the bacteria were "deliberately weakened" by altering their ability to uptake iron. BUT... Casadaban, the scientist, had a genetic blood condition, haemochromatosis, which caused him to have increased levels of iron. Organisms which entered his body through contact in the lab received a boost of strength from his iron rich blood, and he died within a few days of becoming ill.
For some reason, he didn't inform his doctors that he worked with these particular bacteria. Sadly, his life could have been saved had the doctors known and treated him with the right antibiotics.
There's a lesson to be learned from this story. Not quite sure what it is yet, but I'm certain it's there.
RIP Malcolm Casabadan.