Arnold Brown is a minor character in The Evil Within. He appears on one of the missing persons posters, specifically Chapter 11: Reunion Poster 10. Where to find it: Once you are forced to go to the Safe Haven in this chapter, go look on the bulletin board to find this poster.
He was a Krimson City police inspector before he went missing. He apparently claimed that he was holding evidence about an unsolved case before he disappeared.
His death
There is a secret in the The Assignment, where you can find Arnold's dead body. After you fall down and fight Shade you find his dead body among the fallen rubble.
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Arnold's corpse
Upon closer inspection he seems to be bleeding from the eyes, just like the dead patients from Beacon that were sent into STEM. Ruvik killed them causing their eyes to bleed.