I recently found out that in the series, somewhere at the end of season 2, that Shane turned into a walker without being bit, and later Rick tells the group of what Dr Jenner had earlier confessed to Rick in private, that they "all had it in them", and by default all the dead would turn into walkers.
This contradicts the scene in the first episode, where hundreds of dead were lined up at the entrance of the hospital, where Rick was admitted wen he was shot. Why do they not turn ?
So is this a mistake ? Or is there a timeline event where all got infected after a certain period.
PS: I have not read the graphic novels and have completed season 3.