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I'm very positive my stepson has this and I think you're right about Lanza

Alexithymia seens to be characterized by a "lack of imagination":

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That conflicts with the fact that Adam spent most of his time in his own "private world" and had a certain degree of preoccupation for dreams and imaginal constructs:

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What's the big deal? Many people have it. Most killers seem to have it. People with depression, Asperger's, NPD, ASPD and schizophrenia spectrum disorders often have it to some degree. Adam was diagnosed with Asperger's, appears to have been depressed and has even been speculated by some (including Peter Langman) to have had schizophrenia, so it's not very surprising.