Mike visits the house in attempt to assassinate Duane Chow before he can rat on Mike and Walter. However, upon arriving he suspects that someone else has gotten there first, and indeed Chris Mara came and killed Chow on orders from Lydia Rodarte-Quayle and was about to kill Mike as well. Before Mara can convince Mike to spare him, Mike shoots him and leaves a blood splatter on the walls.

Presumably, he cleaned the carnage before authorities discovered the killings. ("Madrigal")

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