(CNN) -- Navy Yard gunman Aaron Alexis left a trail of so-called red flags that, in hindsight, seem quite glaring, even if the impetus for this week's deadly rampage remains murky. For almost 10 years, he showed that he was troubled -- and had a predilection for violence -- even if friends and family members familiar with his emotional problems seem floored that he was disturbed enough to shoot and kill 12 people in Washington on Monday. They may seem like minor episodes when compared with Monday's shootings, but when pieced together, they provide ample fodder for critics who question how Alexis maintained the security clearance that gave him access to the Navy Yard.
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Numerous incidents in Aaron Alexis' past show that he was troubled, prone to violence
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Alexis shooting out the tires of car in Seattle in 2004 is the first in a string of instances
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2010 brings another arrest after Alexis fires a bullet through the ceiling of an apartment
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Last month, two years after his Navy discharge, he tells police he heard voices in three hotels
His father told @placeholder police that Alexis had post-traumatic stress disorder after working as "an active participant in rescue attempts" after the 9/11 attacks, the report said.