Harry knows. Or at least that's what he thinks: 'He knows what's up and he's been on to it for years.' And for years he was a no body. Until he was approached by a discreet agency that requested his help in what he knew. Harry wasn't anything special but his searching for information had allowed him to hear things.
Because of what he knew he was a doomsday prepper and because of that he was prepared for the apocalypse.
He contacted the agency when it all went down. Suggested it may have been something to do with the Corporation. They denied it at least that's not what their sources said. Regardless, Harry continued to head up his own private searches... And as the outbreak worsened, Harry was eventually offered as position at the agency-- which he denied at first because they had refused to believe some of the rumors Harry was trying to spread about the Potius Cras Corpration but after his wife was killed he presumed because she disappeared in Europe he agreed to come on and help. If it was Potius Cras that caused any of this, he was going to find out for himself, and he was going to kill anyone who stopped him, he still suspected that they may have had taken his wife, as they had taken her blood and tissue samples at a clinic when the outbreak first started claiming that they were doctors under a false pretense. Then when they were in hiding one day she disappeared.