Chief Irons is a serial killer who became more unhinged as Racc00n City further plummeted into chaos with the virus and shyt Umbrella caused. It goes back to the first game where everything started in the mountains at the mansion. Since he was corrupted by working with Umbrella through kidnapping children for experimentation and all kinds of bullshyt (hence his involvement in the orphanage), he tried to have everything covered up. Even after S.T.A.R.S. was dispatched to investigate, he had them disbanded in hopes keeping Umbrella's shyt under wraps. Since all of that failed and people were dying on a major scale, he lost it.
An example of him losing his shyt was when he ordered the R.P.D. officers during the initial stages of the outbreak to spread out all of the weapons and resources to random locations in the police station because he thought that he turned into a zombie and that zombies wouldn't possess the necessary intelligence to find weapons through puzzles and other complicated machinations. To be honest, how he convinced them to do some dumb shyt like that is crazy but I guess they were just following orders
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The dead girl in the orphanage is the mayor of Racc00n City's daughter, Katherine Warren. Michael Warren's (the father/mayor) p*ssy ass left his daughter in Racc00n City and escaped. He left her with Chief Irons with the expectation that she'd be protected. In the original game, Claire actually comes across the murder right after Irons killed her and he lied and said that she was infected or some shyt so she wouldn't suspect foul play. In the remake, she was already killed for some time and filled with embalming fluid for display since Irons is into taxidermy. In the remake there's a taxidermy log that you can read which accounts for each of Irons's kills. After killing an animal he talks about almost busting a nut
and his last entry of the log is describing him killing a "female 22 year old pig" which is referring to Katherine Warren. This shyt in the remake is definitely sadistic and dark. There is also free DLC coming out call Ghost Survivors which will have you play as Kendo, Katherine Warren and a USS operative/soldier so I suspect we will get more of a backstory on the events leading up to Katherine's death.